Until I can resolve my high idle issue, I was wondering if there is any way I can manually keep the idle down during the initial start up / cold start sequence? And yes, I realize the computer controls the idle speed.
Here’s the problem:
85 GT- when cold it will very quickly go into a fast idle (as it should) but by fast idle I mean 2800 rpm! It will stay this way for 4-5 minutes and then will eventually settle down to about 1400 at idle and 1250 in Drive. I could live with it but I know it’s not right and I don’t like the engine idling so dang fast when it’s cold, the oil is thick and the engine is not up to normal operating temperature. 🙁
I’ve looked hard and long for vacuum leaks but can’t find any. Which leads me to my next point. The engine runs great, no roughness, no hesitation, missing, etc.
I’m certainly open to ideas about the root cause but until it’s resolved, I’m curious if I can somehow override the computer and FORCE the engine to idle lower when cold. Can it be done? How can I do it?
Thanks, Kit

[This message has been edited by Kitskaboodle (edited 04-15-2025).]

Short answer, no, you need to find the root cause. A diagnostic step, you can have the car running (doesn't matter what rpm), and cover the throttle body with your hand out something that seals, it needs to seal it 100%, if the car dies immediately, no vacuum leak, the issue is with the computer control IAC system somewhere (could be coolant temp sensor or other things) if it continues to run, even if it's significantly slower, then you have a decent vacuum leak somewhere.

Putting the ECM into diag mode will target 1000 rpm idle (as well as fixing the timing to base), but that is a workaround and not a solution, if you have a vacuum leak, it might not even be able to go that low. What is the rpm when hot?

Did You Replace the Engine Coolant Temperature Sensor for ECM?

GM 25036979

Many members didn't get a 14/15 code and reported a "high idle issue" that was a 'mystery'. By replacing this sensor, their idle problems were solved...

------------------
Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 04-15-2025).]

High idle could most likely be a vacuum leak or a defective sensor or IAC valve. The ECM sets the idle speed higher from sensor inputs when cold and it cuts the speed down as the engine reaches operating temperature. Check the IAC, coolant and air temperature sensors,

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Thanks for all the input guys. 😊
Ok, I will remove rubber snorkel
at throttle body, start car, cover throttle body with damp towel / rag and see how she responds.
Coolant sensor? I replaced that with a Rodney low temp one about 60-70K ago. As for the iac, I replaced it about 6-8K ago. Air temp sensor? Isn’t that the one that screws in to the side of the air cleaner housing?
As far as confirming the coolant sensor and air temp sensor, can I test & confirm these with a multimeter? What should be the reading for both?
Kit

quote Originally posted by Kitskaboodle: Thanks for all the input guys. 😊 Ok, I will remove rubber snorkel at throttle body, start car, cover throttle body with damp towel / rag and see how she responds. Coolant sensor? I replaced that with a Rodney low temp one about 60-70K ago. As for the iac, I replaced it about 6-8K ago. Air temp sensor? Isn’t that the one that screws in to the side of the air cleaner housing? As far as confirming the coolant sensor and air temp sensor, can I test & confirm these with a multimeter? What should be the reading for both? Kit

The coolant temperature sensor and the cooling fan switch are in the same area on a 2.8L. Rodney sells a low temperature coolant fan switch. If you put the cooling fan switch in the location for the CTS that may cause problems. The ambient air temp sensor is the one that sits on the air filter box. You can test sensors by measuring the resistance with a multimeter but you should have some fairly hot water available to take sensor readings at both ends of the spectrum.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by Kitskaboodle: Coolant sensor? I replaced that with a Rodney low temp one about 60-70K ago.

That makes no sense... as Dennis has addressed above.

If either the CTS or the IAT are reporting low (actual or incorrect) temperatures to the ECU, a high idle speed will result. Either test the resistance of these sensors as mentioned above... or use WinALDL (or a scanner) to see in real time what the temperature readings are. When I've tested mine, I've done it first thing in the morning after the engine has sat all night. With the ignition key turned to RUN and the engine not running, the temperature readings from both sensors should be within a few degrees of each other, and basically the same as the ambient air temperature around the car.

quote Coolant sensor? I replaced that with a Rodney low temp one about 60-70K ago.

You're confused as Rodney unit is a low temp fan switch...

You need to check the sensor which sends a signal to the Engine Control Module {ECM}


If you want to try to test than replace...


BTW - Members have reported that their "High Idle" problem was solved by replacing this sensor.

quote ketstang: I replaced the engine coolant temperature {sensor} for the ECM and initially didn't think it solved my high idle problem, but after driving about 100 miles with the new sensor the idle has settled down to 800-900rpm. I am so happy to have finally found a solution. Thanks

[This message has been edited by Vintage-Nut (edited 04-15-2025).]

You guys are a huge help!
Thanks for the coolant sensor correction. Actually, I knew you guys were saying coolant sensor but in my head I was thinking “fan switch”. (sorry, I’m getting old 🙁) Anyways, that GM resistance: ohm chart is a keeper for future testing. 😌 I will let you guys know what I come up with.
In the meantime, about an hour ago I did go out and do the first test we discussed above. As an fyi, there’s a right way and a wrong way to starve the engine of air. I initially took about 4 shop towels, folded them into a square and tried to seal off the throttle body but it was still breathing right through that wad of shop towels. (even wetting them didn’t help) So, I got a small, flat piece of wood + 1 folded shop towel, then sealed off the throttle body opening and the engine died immediately. So, as said above, that confirms I don’t have any vacuum leaks, correct?
Kit

quote I got a small, flat piece of wood + 1 folded shop towel, then sealed off the throttle body opening and the engine died immediately. So, as said above, that confirms I don’t have any vacuum leaks, correct?

I read a different test than sealing the throttle body but I never tried it....

quote Check for vacuum leaks by covering the IAC inlet passage inside the bore of the throttle body with your finger If the engine continues to run at ANY RPM, you do indeed have a vacuum leak

I verified my vacuum system by disconnecting each line by capping/sealing one end; attached a hand operated vacuum pump with a gauge on the other end; pulled-out the atmospheric pressure to 20 inch-Hg and hold the pressure for 5 minutes. If the pressure didn't rise, the line didn't have any leaks...

[This message has been edited by Vintage-Nut (edited 04-15-2025).]

Question for Kit....

On the throttle body, beside the throttle linkage cam there should be a very small (1/4") plug that covers a setscrew.
The setscrew was used at the factory to set idle speed and then plugged.

If the plug is missing, chances are someone has been messing with the setscrew.

I do not recommend messing with the setscrew unless every other cause for high idle has been eliminated.

(Edited to correct improper information.)

[This message has been edited by olejoedad (edited 04-16-2025).]

mines a 2.5 which is different but mine had a problem where it idled at 2600 rpm.id go five miles away to eat and the idle stayed at 2600 til i got there.when i left the idle would drop down to almost normal.i changed the idle air solinold and its idled at around 1100 since.

Thanks again for all the additional input.
As Vintage-Nut mentioned above, it’s a good idea to check or replace the coolant sensor as top priority. I haven’t tested it yet but since they’re relatively cheap, I went ahead and ordered one from Amazon. I’ll update you all later on this.
OldJoeDad: I have never touched that plug on top of the plenum. Ironically, the plenum I have in the car was from a member in Oregon who used to do a plenum / manifold powder coating service. His name is “Electrathon”. I had to double check it and the powder coated replacement I got from him is indeed capped. Kit

[This message has been edited by Kitskaboodle (edited 04-15-2025).]

quote Originally posted by Kitskaboodle: OldJoeDad: I have never touched that plug on top of the plenum. Ironically, the plenum I have in the car was from a member in Oregon who used to do a plenum / manifold powder coating service. His name is “Electrathon”. I had to double check it and the powder coated replacement I got from him is indeed capped.

You have a powder-coated throttle body? That's where the set screw is located that has a cap over it from the factory.

quote Originally posted by Patrick: You have a powder-coated throttle body? That's where the set screw is located that has a cap over it from the factory.

You're correct, Patrick. The plugged off idle adjustment screw is on the throttle body, not the upper plenum.

My bad. Thank you for pointing out my error.

I have edited my post to reflect the proper information.

I seldom look at the stock Fiero engines, I see more swapped engines.

I figured the adjustment screw was worth a mention, however, as no one else had brought it up in the conversation.

I'm surprised no one else thought to bring it up as a possibility.

quote Originally posted by olejoedad: I figured the adjustment screw was worth a mention, however, as no one else had brought it up in the conversation. I'm surprised no one else thought to bring it up as a possibility.

To be honest, it seems like such an obvious thing to check, and it has been mentioned a thousand times previously in these forums (and everybody checks the old threads, right? )... that I guess it's easy to overlook mentioning it yet again. But yes, it was definitely worthwhile for you to bring up in case Kit was unaware of this possible cause of a high idle speed.

quote I figured the adjustment screw was worth a mention, however, as no one else had brought it up in the conversation. I'm surprised no one else thought to bring it up as a possibility.

Because to me, it is the last thing to do....

quote Originally posted by olejoedad: If the plug is missing, chances are someone has been messing with the setscrew. I do not recommend messing with the setscrew unless every other cause for high idle has been eliminated. (Edited to correct improper information.)

Which is why I stated the above.

Oops…I stand corrected again. 🙁 (I told you guys I’m getting old - or as George Burns once said, “you’re only as old as the girls you feel” 😀)
Yes, the throttle body is not powder coated! 😀
Anyways, here’s a pic to show you my engine. You can barely make it out but if you look hard you can see that the plug is there on the throttle body. Kit

quote Originally posted by Kitskaboodle: Anyways, here’s a pic to show you my engine.

Well, I can see the problem quite easily now... your engine is just too damn clean.

Update: Since new sensors are quite cheap (about $20-22 + free shipping for the Delphi brand) I decided to just go ahead and replace them both. (coolant sensor and IAT sensor) I did this also for peace of mind.

Anyways, after installing them I started the engine (sitting all night) and the engine went right to about 2500 rpm. (300 less than before) It stayed at 2500 for about 4 + minutes. After the engine was fully warm, the idle went down to about 1400 rpm. After driving it for about 10 minutes around the block and then letting it idle for another 5 minutes, it eventually went down to about 1250-1300 rpm.

It looks like for now I’m just going to have to live with it. 🙁 Can we now talk about the IAC? I’m almost certain I replaced mine about 10-12K miles ago. (I think it was Standard brand) As I recall, when I installed it the idle was crazy high.I posted a thread here and a fellow member told me the sequence of how to “re-set” it. He was exactly correct! After I did the sequence, the idle went down to normal.
How do I verify the IAC that it’s working properly?
Kit

[This message has been edited by Kitskaboodle (edited 04-17-2025).]

How can you test the IAC by MordacP
https://www.fiero.nl/forum/...110502-2-093097.html

quote Chicken McNizzle: The following is based of course on a clean idle air passage as well as a butterfly that has never been tampered with.... 1. Key on Engine off, place jumper wire into ALDL to put vehicle into diagnostic mode ( to check codes ) 2. Go to engine bay, you will hear stepper motor moving in the IAC, remove IAC connector. At this point the IAC will be fully closed therby blocking the IAC passage and the car should not start 3a. IF CAR STARTS - Attempt to start car - if car starts and runs then there is a vacuum leak and/or tampered throttlebody and the butterfly will have to be reset. 3b. IF NO START - Attempt to start the car - If the vehicle does not start then the IAC is functioning 4. Reconnect IAC connector and remove jumper wire from ALDL and start car, there will be fluctuations in starting and even hesitation, and in some cases no start as the IAC resets itself. This test confirms: - That the IAC is functioning - test for vacuum leaks - test for a tampered throttle body

quote Originally posted by Kitskaboodle: Oops…I stand corrected again. 🙁 (I told you guys I’m getting old - or as George Burns once said, “you’re only as old as the girls you feel” 😀) Yes, the throttle body is not powder coated! 😀 Anyways, here’s a pic to show you my engine. You can barely make it out but if you look hard you can see that the plug is there on the throttle body. Kit

Speaking of OLD and throttle bodies... I remember having a conversation (EDIT, back in 1997) with some people on a car forum on UseNet via a BBS, and I was telling them that the Fiero's V6 throttle body was made by Holley. They swore up and down that either someone replaced it with an aftermarket one, or that I was lying through my teeth... saying Holley would never make a factory part for a lowly car like the Fiero. Alas, there was almost no internet back then, no normal person had a digital camera, I had no scanner or Polaroid, and there was no way to upload images to the message board, other than via Zmodem or Xmodem or something, but couldn't attach them to a message. So I just had to take it.

[This message has been edited by 82-T/A [At Work] (edited 04-18-2025).]

Ok, since a quality IAC is only $38.00 from Amazon, I decided to just buy a new one and I’ll keep the old one as a spare. See pic below of the new one.
On a different note….. how exactly do you “reset” a Fiero IAC? One thing is almost certain: after I put the new one on, the rpm’s are going to be very high and I will need to bring it down asap. By the way, there is a paper instruction thingie with the new IAC and it said that for Pontiac’s, the IAC will reset itself after you drive over 40 mph. Is that correct?? Kit

[This message has been edited by Kitskaboodle (edited 04-19-2025).]

quote there is a paper instruction thingie with the new IAC and it said that for Pontiac’s, the IAC will reset itself after you drive over 40 mph. Is that correct??

YES, but you need to check if it needs to be set properly before installing it...


PS - I added more IAC information...
http://www.calgaryfieros.com/OSGdocs/IAC.html
------------------
Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 04-19-2025).]

Thanks again for the reminder about setting pintle length.
I measured the new one and it is pretty close to 1 and 1/16th so I’m under the magic 1 and 1/8ths.😊 So, I’m going to install it as-is. Lastly, I read all the threads that pertain to iac resetting so I got it down now. I will report back tomorrow and let you all know if my high idle (when cold) lowers any from what is is now. (2450-2500 when I first start it - it will fast idle like this for at least 4 minutes) 🙁 Kit

[This message has been edited by Kitskaboodle (edited 04-19-2025).]

High idle could most likely be a vacuum leak or a defective sensor or IAC valve.

I’ve looked high and low for vacuum leaks and can’t find any. Per a suggestion above, I did verify that after blocking off the throttle body suddenly with a piece of flat wood, the engine immediately died. Since beginning this thread (and per the recommendations above, I have now replaced the coolant sensor, IAT sensor and today I will be replacing the IAC. I will report back later today.
Thanks again for all the input. 😊 Kit

[This message has been edited by Kitskaboodle (edited 04-20-2025).]

Do you know for sure if you have a factory ECM and the correct PROM?

I was in another thread and I mentioned this:

The ECM Model number must match:
Fiero Model
Year
Engine Size

The PROM in the ECM has a Model number and it must match:
The Tire Sizes
The Emissions: Federal or California
Transmission Type: Manual or Automatic
Transmission Gear Ratios (part of the Transmission Model)

If you have the correct ECM but the PROM is wrong, this could effect the Idle Speed which, on your Fiero, should be about 900 RPM fully warmed up with slight wavering plus or minus 50 RPM.

How the O2 Sensor is working can effect idle. An engine may run well with one that us starting to go or another problem may be present.

Here is a simple go/no go test:

Cold start.
Put the ECM in DMDIAG Mode (the Paperclip Trick).
Start the car (do not drive in this mode as the Timing Advance is disabled so you can set the timing to 10 degrees BTDC and not fight the ECM).
The Idle is forced to 1000 RPM (to help calibrate the Tachometer).
The SES should blink rapidly to indicate the ECM is in Open Loop.
After a few minutes, the O2 Sensor should be warm enough to start operating. This is when the ECM will go into Closed Loop.
In Closed Loop the SES should blink slowly (on and off every couple of seconds). The ECU constantly wavers the Air Fuel Ratio (AFR) slightly to make sure the O2 sensor is working and responding properly. When the light is on, the AFR is above 14.7 : 1 stoichiometric, and off when below that. So not only should it blink on and off slowly every second or so, it should also be about a 50% duty cycle on average. It's not perfect, but if it is not on and off about the same amount (50% duty cycle), something is effecting the idle AFR and that is a clue to a malfunction somewhere - possibly a sluggish O2 Sensor, or EGR Subsystem issue, dirty IAC Valve pintle and seat, flaky CTS Sensor. But you will be amazed on what other things that can effect Idle. One thing overlooked... a PCV Value... they get so oil fouled at times.

------------------
Paul Romsky

Thanks for the input Paul. You brought up some interesting things. This high idle issue has not always been there so I don’t think it’s computer related. Believe it or not, I change my 02 sensor every two years right before I get my smog test. Regarding a clogged pcv valve: would that apply in my situation since it does initially go high when cold (2500 rpm) but it does eventually go down to about 1400.

On a different note, I put in the new IAC today and basically it made no difference. It still idles at 2450-2500 when cold, takes a good 4+ minutes to go down and even so, it will only go to go 1350-1400 idle and about 1250 in drive. This is as low as it gets. 🙁
Here’s what I have done thus far:
Verified that engine dies immediately if I suddenly block off the throttle body opening
Replaced coolant sensor
Replaced IAT
Replaced IAC (Gumout used in IAC passage, proper reset done and drove it on freeway for about 30 minutes.
Not sure what to do next..,, 🙁
Kit

[This message has been edited by Kitskaboodle (edited 04-20-2025).]

quote Originally posted by Kitskaboodle: Verified that engine dies immediately if I suddenly block off the throttle body opening

That's fine for addressing concerns of a vacuum leak downstream from the TB. The problem with that method is that it doesn't tell you if the throttle blade itself is actually closing far enough. Instead of covering the entire mouth of the TB, just use your finger to block the port in the mouth of the TB that supplies air to the IAC valve.



The engine should stall. If it doesn't, I'd suspect that the idle stop screw is misadjusted (or the throttle linkage is hanging up somewhere). If it does stall, then see below.

quote Originally posted by Kitskaboodle: Replaced.... Replaced... Replaced...

Kit...The problem, as I see it, is that you're not investigating what if any difference the new sensors are doing in regards to the actual info they're sending the ECU. If you don't use a scanner or WinALDL, you're flying blind. It's possible for example that the new CTS or IAT sensor is telling the ECU that it's -40°. I'm not trying to give you a bad time, but it's the reality of the situation. You need to know what the ECU is being told. It's even possible the wiring harness has an issue which is preventing one or more sensors from telling the ECU anything. In theory a code should be set if that's the case, but I'd want to know for sure what's going on.

[This message has been edited by Patrick (edited 04-20-2025).]

Did You Test or Replaced the MAP Sensor?

This sensor cannot be cleaned or repaired; it either works or doesn't.

Manifold Absolute Pressure Sensor TEST with a hand pump...


BTW
GM discontinued the original MAP and revised the sensor years ago; so, if you have the original, get the newer sensor which is more accurate.

The GM part number for this revised map sensor is 12569240 {ACDelco part number 213-1545}

To me, don't buy a cheap aftermarket unit, get a genuine GM MAP...

Incorrect V6 Idle List


PS - Any EGR leakage will play havoc with idle; confirm that your EGR is really closing.

------------------
Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 04-21-2025).]

Kit,

It might feel like we are coming at you from all sides, well, we kind of are - from all over the world [smile]. But it's just hard for a bunch of people to make suggestions in a forum. If we were all there with you, this would be a whole bunch simpler. If someone tells you to do something you already did, just ignore it [smile] It's happens to all of us. Hang in there, we will do our best to help you.

I saw your list and you seem to be doing the right things so far. One of the things about this site, I can't see any of the message as I type a reply, so I can't keep the whole thread in my head, so I might get redundant or miss something.

There is a lot more things to look at, but I try to suggest the simpler things first. I am a "pull it and bench test it" kind of guy... I don't like to "replace things until it works".

I believe you when you say there are no vacuum leaks. I am old school and used the carb cleaner trick to find leaks... effective but DANGEROUS - don't do it. They now make fog generators that are very safe and can help find the more subtle leaks. Look into them but don't buy one just yet.

You are in the right area:
Throttle Body:
Throttle Plate: closed/open/sticky/dirty/obstructed/loose-worn bearing
IAC: Valve Seat clean and IAC Unit replaced (hard to test on the bench without using an Arduino UNO and a stepper motor driver).
TPS: Adjusted properly, not noisy (signal wise), not sticky. I can tell you how to bench test one (even if it is new... we see a lot of failed out of the box these days).
Cold Start Fuel Valve and it's Temperature Switch (near the Fan Switch). The injector can leak, the Switch can get flaky. A bit involved to bench test the Injector.
MAP Sensor: Can tell you how to bench test it.
EGR Solenoid: Again, bench testing may help rule it out.
EGR Valve, I agree with the others, a subtle leak or stuck valve can affect Idle. I have instructions on bench testing the EGR system.
CTS: You replaced it. I recommend bench testing first it before installing - we can revisit that later.
IAT: You replaced it. Bench test first - but we can revisit that later too if needed.
PCV Valve: Involved to bench test, not expensive, best to replace at every tuneup before emissions... California or Federal?
Fan Switch: Most likely not and issue with idle, but you need to make sure it is working. There are 2 Fans: one on the Radiator, one behind the rear trunk liner on the passenger side. This hidden fan keeps the Ignition Coil and Alternator cool. Critters like to build nests in the fan. I have tips to prevent that. Needs to be checked yearly.
Air Filter: I think you have that covered.
Coolant Thermostat: Involved to bench test. Watch your dash Temperature Guage, but don't rely on it. The guage is driven by the ETS (Engine Temperature Sensor) on the head near the distributor. It's is separate from the CTS.
If you have Cruise Control, is it functioning properly? A subtle leak here could affect idle in rare cases.
I don't think you need to look at the Ignition System yet.

Now the harder things to put off on checking until everything else is ruled out.

Fuel Pump: Not working efficiently. Too difficult to remove for normal bench testing.
Fuel Pressure: Not around 40 PSI +/- 5. Wider tolerance may be ok.
Fuel injector: Leaky. Involved to get at and more involved to bench test.

Having a scan tool is vital in diagnostics. Many of the sensors can be ruled out by using a good one.

I designed the Fiero GT ALDL Monitor Adapter that is sold from The Fiero Store. The GUI software is free to download and to look at, but the Adapter costs $84.95. Be careful with any ALDL Tool. They can only give you indications, they usually don't solve all problems, but they help. Fieros don't have OBD-II, so the ALDL is all we have.

If you have the budget and you buy my Adapter, I will help you as much as I can using the tool and what it is telling you. If money is tight, I don't recommend buying it.

I am in New Hampshire USA in the eastern time zone. I am available for free phone consultations from 9AM to 9PM 7 days a week, but send me an email first to set up a phone call. You pay for the call.

My email is on my webpage:


Paul Romsky Fiero GT ALDL Monitor


Paul
+1(603)465-7225
------------------
Paul Romsky

[This message has been edited by Romsk (edited 04-21-2025).]

Wow, you guys are tag teaming me. But, I say that it’s a good thing. 😊
Hope I can remember all that was said above.
Patrick- yes, you’re correct. I can test things rather than simply replace but I just wanted to be done with it and was hoping my “quick fixes”would work.
Funny interjection here: my dad was an aircraft engine inspector for United Airlines SFO and so I heard a lot of stuff from him that he learned and wanted to school me on. I always remembered this saying: “There’s never enough time to do it right, but there’s always enough time to do it over”. Hmmm, I think that applies to my Fiero method of repair technique. 🙁
Ok, on to business….
Patrick- I was thinking that very thing yesterday about the possibility of the throttle body butterfly not closing all the way. So, I examined the opening and looked closely top and bottom while turning the throttle shaft and it seems to be fully closing. While I had the rubber snorkel off I decided to hit the throat area with Gumout and also hit the orifice hole. At this point I did not start the car yet as I was also in the process of removing, cleaning and testing the pcv valve as mentioned above. (doesn’t hurt to check it) After hitting it with Gumout, I made sure the barrel doohickey rattled around inside. Then I did the blow test. Here’s the weird part: as you know it’s supposed to allow air one direction only but I noticed it will still occasionally blow in both directions. I think that barrel thingy doesn’t always seat properly. (a little flaky?) Anyways, since a metal AC Delco is only $6 bucks, I’m just going to put in a new one. This is where I stopped for the day. I will get the pcv valve tomorrow afternoon. As soon as I get it I will install it and then start car (from cold) and put my finger over the hole in the throttle body and see if it dies and then report back.
Vintage- Nut: I do have 3 spare MAP’s. One is an
good used GM factory one but I don’t see a GM p/n on it. I will do a swap tomorrow and see what the fully warm idle it is. (right now it’s 1400 when fully warm)
Paul: Strangely enough, I tried to buy the scan tool from the FieroStore website about 4-5 months ago and I didn’t see it. Today I looked and now they have it again. It’s gone up to the tune of $114.95 🙁 Cooling system is fine. Car runs consistently cool / normal. Thermostat is ok. Fan has been upgraded to electric and comes on no problem. Water pump is brand new as well as the fuel pressure regulator. As for the tach, it’s always been consistent as far as I know and in the past I installed Rodney’s tach filter. Actually, I do have a timing light with a built in tach but I’ve not used it on this car.
After I do all that I said above, I want to address the egr valve as you guys pointed to. I do have a Mighty Mite vacuum gauge / Kit. So, when the engine is cold, is the egr supposed to be open or closed? And obviously, I can’t verify whether it’s open or closed when it’s bolted to the exhaust.
No, on my egr you cannot really see the plunger in action.
Thanks everyone for your input!! 😊
Kit

[This message has been edited by Kitskaboodle (edited 04-21-2025).]

quote Originally posted by Kitskaboodle: I was thinking that very thing yesterday about the possibility of the throttle body butterfly not closing all the way. So, I examined the opening and looked closely top and bottom while turning the throttle shaft and it seems to be fully closing.

There's no way the engine is going to be idling at all unless air is getting in somewhere. Since you already know that there is no vacuum leak downstream of the TB, plugging the IAC port with your finger will tell you whether the unwanted air is getting past the throttle blade. If the engine stalls with the IAC port blocked, then you'll know for sure that the IAC valve is letting too much air in... for reasons yet to be determined.

quote Originally posted by Kitskaboodle: I want to address the egr valve as you guys pointed to. I do have a Mighty Mite vacuum gauge / Kit. So, when the engine is cold, is the egr supposed to be open or closed? And obviously, I can’t verify whether it’s open or closed when it’s bolted to the exhaust. No, on my egr you cannot really see the plunger in action.

The EGR valve only opens under certain conditions while driving. On the OEM style EGR valves, you can actually open the valve by hand by sticking a finger up through a hole on the underside of the valve housing and pushing the valve open. The engine will stumble (while idling). If your EGR valve does not have the holes in the underside of the EGR housing, a vacuum pump will open the valve... and again, the engine should stumble. However, I don't feel your elevated idle RPM speed is EGR related.

[This message has been edited by Patrick (edited 04-22-2025).]

quote is the egr {valve} supposed to be open or closed {at idle?}

Closed

quote And obviously, I can’t verify whether it’s open or closed when it’s bolted to the exhaust. No, on my egr you cannot really see the plunger in action.

Yes, you can't verify if it’s stuck open due to carbon deposits when it’s bolted to the exhaust, BUT you can check the diaphragm "in action"..

While the engine is cold:
*Remove the vacuum line from the EGR vacuum port
*Connect your hand held vacuum pump with gauge on the EGR vacuum port
*Apply vacuum and observe the EGR diaphragm/valve, the valve should move up
*Hold the pressure a minute or two...the pressure must hold / if not, the diaphragm has a hole and replace the EGR valve.

If you need to replace the EGR valve:
How to Replace Your V6 EGR Valve - Step by Step by Bloozberry
https://www.fiero.nl/forum/Forum9/HTML/000033.html

[This message has been edited by Vintage-Nut (edited 04-21-2025).]

Kit,

My adapter is the $84.95 one. It is called the Fiero GT ALDL Monitor.

86-88 V6 ECM ALDL Monitor Tool

[This message has been edited by Romsk (edited 04-22-2025).]