88 2M4 5spd

Same problem driving me insane!!!

May be a coincidence, but it seems to run okay in the morning on the way to work and out for a quick lunch. Usually not much traffic. However, on the way home bumper to bumper stop and go traffic. This is when generally acts up.

Sitting and idling the tach is pegged right around 1000. Then it will start fluctuating between 900 - 1100/1200. Then will start dropping as to almost cutting off, then catch itself, drop, catch a few more times then cut-off. Usually, I catch it dropping, play with the gas to keep up the rpm's a bit. But when I start to go, drops on its face. A lot of times, turn the key off, start right back up as if nothing happened. Could be for a half of a minute to several until it starts back all over again. I've stopped several time to reset the IAC, seems to work for a while, again, maybe a coincidence. I've just replaced plugs, wires, PVC, IAC,TPS, EGR, air filter & crankcase filter. (Problem existed prior).

Any ideas.

Thanx again,

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Always
Loved
Fieros

Man, that blows.
Well screams Defective IAC to me big time at 1st buuuut.....

ICM BIIIG time check that. Check the wire connectors that connect to the ICM are not pinched by the dizzy cap or the connector to ICM is corroded or a wire is bad to ICM.
Auto Parts store can test the ICM for you. The more I think about this the more it seems to be an ICM related issue.
Could also be a going Ignition Coil or corroded Coil Connectors or bad wire. That is also screaming as probable issue dude.
If it was an auto I'd def say sticking solenoid for tcc.
Check ALL vacuum lines and connections are groovy as well and the 'coffee can' ain't all rusted out. (vacuum canister)

Hope this helps

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Put the blow torch down please, its just a Fiero.

The 88 Duke does not use a distributor. It uses a crank position sensor and coil pack ignition.

If you have access to a scan tool, or can take it somewhere to have the ECM scanned, that is the best place to start.

I noticed that you did not mention the MAP sensor. A bad MAP will cause drivability problems.

I don't know anything about DIS but when my car was doing that it turned out to be the coil.
It would get hot and short, but when it was cold it would run fine.
back then it was a $15 part, don't know about the 88 or the price now.

quote Originally posted by tntcary: Man, that blows. Well screams Defective IAC to me big time at 1st buuuut..... ICM BIIIG time check that. Check the wire connectors that connect to the ICM are not pinched by the dizzy cap or the connector to ICM is corroded or a wire is bad to ICM. Auto Parts store can test the ICM for you. The more I think about this the more it seems to be an ICM related issue. Could also be a going Ignition Coil or corroded Coil Connectors or bad wire. That is also screaming as probable issue dude. If it was an auto I'd def say sticking solenoid for tcc. Check ALL vacuum lines and connections are groovy as well and the 'coffee can' ain't all rusted out. (vacuum canister) Hope this helps

Thanx for the input.

I didn't mention that I did put new vacuum lines on. I don't see, hear or feel anything out of the norm. I was wondering about that canister as well because the cruise went out a little while ago. This morning I started to pull a line off of the canister and the vacuum started to relieve. So I guess that's out.

I pulled the wire on the IAC while it was running and no change, so I'm assuming it's okay.

I'm going to pull the ECM and have it checked within the next day or so.

Just thinking out loud on the following possibilities/rule outs:
- coil(s) getting hot. Wouldn't that create a miss fire on 1&4 or 2&3. Doesn't seem to be doing that.
- fuel pump?? seems to run fine on the highway moving. Not bogging down or anything of the like.
- fuel injector??? possible
- TBI rebuild time

Could be wrong but I really think that it's electronic fuel related.

Also, I noticed that there seems to be no vacuum to the EGR. Should there be continuous vacuum going to the EGR????

Didn't mention that there are no codes thrown either.

Thanx again guys,

OBD-I --- Grrrrrrrrrr!!!!! OBD-II and carburetors work great!!!

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Always
Loved
Fieros

quote Originally posted by olejoedad: The 88 Duke does not use a distributor. It uses a crank position sensor and coil pack ignition. If you have access to a scan tool, or can take it somewhere to have the ECM scanned, that is the best place to start. I noticed that you did not mention the MAP sensor. A bad MAP will cause drivability problems.

Ah, duke, yes my bad. Hello line one to me.
MAP I agree needs to be checked.
Your fuel pressure could be dropping down and causing the issue as well. Fuel pump, filter, the like.
Sticking/bad injector could also be a issue.
Have fuel pressure checked to eliminate that end. How long since a fuel filter replace? Those are awesome easy in a duke. They stare right at you saying change me every time you open deck lid. LOL

[This message has been edited by tntcary (edited 04-28-2013).]

Also, I noticed that there seems to be no vacuum to the EGR. Should there be continuous vacuum going to the EGR????

Ummm, pull the line to the EGR, blow on it, if there is no restriction, then it should be fine, as the vacuum is only there at cruse.
Did you reset the ECM? I always do that after changing sensors to get them to reprogram quicker.
If the problem is the same before as after, then check codes, if no codes, it gets a little difficult to say.

Look at the ECM with TunerPro RT when this is happening and see what is happening.

TunerPro RT - http://tunerpro.net

87 - 88 Fiero .ADX definition for TunerPro - http://www.reddevilriver.com/uploads/87-88_2.5.adx (Right click and "save as") *

USB to ALDL cable - http://www.reddevilriver.com/aldl.html *

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Latest update:
882M4 - 5sp

Just a quick summary: No codes, felt like the air/fuel was being shut off, (sometimes a complete engine off to a barely running). Turn the key off, restart okay for a bit getting progressively and more frequently worse. Reset IAC. Seemed to clear up a while and again return. I tried several places but could find no one to test my ECM. While I was thinking electronic - fuel related I have replaced the following:
- IAC
- TPS
- EGR
- MAP
- PVC
- Coolant sensor
- MAT
- breather element
- air filter
- vacuum lines
- spark plugs
- plug wires
- fuel filter
- fuel pressure regulator
- fuel injector
- oil pressure switch
* also checked the fuel pressure. coming in at 16-18psi at idle or part/full throttle.

Seems like the completely cutting off or pulling down has stopped. The idle hunting is still ongoing, 900-1200 +/-. However, I noticed that it appeared to stumbling at idle and giving it throttle it sounded as if it were missing. Just for fun I put an inductive timing light on 1,2,3 & 4. Definitely missing on all 4 cylinders. So...... I replaced the ICM, CPS, both coils, and cleaned up the grounds. Still missing on all 4 cylinders. Wiggled all of the wires and connections around in the entire engine compartment. Looked at night and could find no flashes/sparks. I have an ECM coming and hope this works. If not, I'm out of options. Anyone else have any other ideas.

BTW: The replacement parts were not a total loss, some needed replacing.

Thanx again,

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Always
Loved
Fieros

the injector? I had a problem where my '88 2.5 would not provide enough gas to stay running. Sometimes it would run fine, but other times it would just die.

Also, maybe you have a bad throttle body gasket, which is letting in extra air.

quote Originally posted by jaskispyder: the injector? I had a problem where my '88 2.5 would not provide enough gas to stay running. Sometimes it would run fine, but other times it would just die. Also, maybe you have a bad throttle body gasket, which is letting in extra air.

Thanks again,

I thought about rebuilding the TBI, and still probably will. But the missing fire on all 4 cylinders has taken me on a different journey for the time being.

weak coil?

quote Originally posted by 2.5: weak coil?

I'm going through every scenario that I can think of and yes that one came to mind also. However, the coils that were on there were about 1½ years old and I just replaced them with two (2) new ones last night, (as well as the ICM & CPS). If just cylinders 2&3 or 1&4 were missing, I'd say that's the problem. But ................. kind of find it hard to believe that 2 coils went bad at the same time and I just received 2 bad ones.

Also, this happened earlier, but just again during lunch. I started it up and turned the AC on. Proceed to go and that thing was bucking like a wild horse. Turned the AC off and it was okay. Turned the AC back on and again, bucking. Also was hard to keep it running. So I turned it back off. After the car warmed up a bit, it ran okay with the AC on.

I'm still hoping and praying it's the ECM.

Thanx,

Have you checked all the engine / chassis grounds? I've heard of people just adding an additional one to fix probs too.

quote Originally posted by 2.5: Have you checked all the engine / chassis grounds? I've heard of people just adding an additional one to fix probs too.

Yes. Last night went through, took them off, sanded/scuffed up and reattached them. I thought about adding one also.

Maybe I should schedule an appointment at the shop. Seems like when you do that as well as the doctor, everything clears up and works.

Thanx,

Where are all your replacement parts made? If you opted for cheap china made parts, they can cause problems...
~ Paul
aka "Tha Driver"

Custom Fiberglass Parts

My favorite place to look is vacuum leaks; there are so many possibilities and they're almost all cheap. Besides the lines there are the rubber connectors, of course, but there are quite a few others that may not be obvious. The valve cover gaskets, the oil fill cap, the PCV grommet and the other one on the other valve cover, the PCV connector which doesn't seem to be available, but can be replaced with a hose loop, the hose to the brake booster and perhaps most relevant in your case, the brake booster itself. It's also important to make sure the connections are tight. For instance, the big pipe that fits into the snorkel has to be pressed very hard to get properly seated.

Disconnect your oxygen sensor and try to replicate your problems. When most O2 sensors fail, they fail with a bias towards the rich side. The computer is seeing this false signal and is trying to lean out the mix, not knowing that the engine is already lean. When the engine is surging and hunting at idle is because the ecu is leaning the mix to the point the engine stalls, the rpm drops below normal run rpm, goes into open loop and fuel is returned to somewhat normal. The ecu will then go back into closed loop mode and the whole process begins again. This could also explain the rough running when the A/C is first turned on before the engine is up to running temp. During these lean excursions, the ecu remembers what it thought was a rich event and is keeping things on the lean side from start-up on.

A O2 sensor can be bench-tested by heating the thimble (tip) with a propane torch to at least 625° F. In this case, the thimble shield should glow a dull cherry red and produce a 0 to 0.9-volt swing as the torch flame is passed across the thimble.


The other check is to make sure the O2 sensor ground is good and that there is the proper voltage present on the O2 sensor feed to the ecu. If the voltage exceeds 1.0 volts, the problem might be caused by a bad oxygen sensor ground or by battery voltage leaking into the O2 sensor input to the ecu. Normal should be around .450 volts with the ignition on. This is a normal bias the ecu applies for O2 sensor testing.

All voltage test should be done with a DIGITAL multimeter.

quote Originally posted by chetw77cruiser: Disconnect your oxygen sensor and try to replicate your problems. When most O2 sensors fail, they fail with a bias towards the rich side. The computer is seeing this false signal and is trying to lean out the mix, not knowing that the engine is already lean. When the engine is surging and hunting at idle is because the ecu is leaning the mix to the point the engine stalls, the rpm drops below normal run rpm, goes into open loop and fuel is returned to somewhat normal. The ecu will then go back into closed loop mode and the whole process begins again. This could also explain the rough running when the A/C is first turned on before the engine is up to running temp. During these lean excursions, the ecu remembers what it thought was a rich event and is keeping things on the lean side from start-up on. A O2 sensor can be bench-tested by heating the thimble (tip) with a propane torch to at least 625° F. In this case, the thimble shield should glow a dull cherry red and produce a 0 to 0.9-volt swing as the torch flame is passed across the thimble. The other check is to make sure the O2 sensor ground is good and that there is the proper voltage present on the O2 sensor feed to the ecu. If the voltage exceeds 1.0 volts, the problem might be caused by a bad oxygen sensor ground or by battery voltage leaking into the O2 sensor input to the ecu. Normal should be around .450 volts with the ignition on. This is a normal bias the ecu applies for O2 sensor testing. All voltage test should be done with a DIGITAL multimeter.

Forgot to mention. New O2 sensor too, but will check it out.

Thanx

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Always
Loved
Fieros

Okay, still battling this ever going problem that seems to be getting better at some points in time, until today. I rebuilt the TBI this afternoon, put it back on and it ran like crap. Would not stay running with out keeping on the gas. By mistake the MAP vacuum line popped off while I was moving the breather. Idle smoothed out and went to normal. It sounded great. I tried to put the vacuum line back on and it tried to stall again. Took it off, ran great. Put my finger over the vacuum port on the TBI, tried to stall again. Wondering if covering the vacuum port would cause the engine to die. As I said previously I did replace the MAP with a new one, which could possibly bad. Wondering if a new one might cure the problem. I'm out of options and just about patients with this never ending problem. Might also take the TBI off and go over it again. I've rebuilt TBI's & carbs before with no problems, but that's always a possibility.

Any thoughts?????

Thanx agai\n,

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Always
Loved
Fieros

It sure sounds vacuum-related. Could the vacuum lines be mixed up? Could there be an obstruction in the snorkel? Maybe it's getting air through the vacuum connection because it can't get enough through the snorkel.

quote Originally posted by 85 SE VIN 9: It sure sounds vacuum-related. Could the vacuum lines be mixed up? Could there be an obstruction in the snorkel? Maybe it's getting air through the vacuum connection because it can't get enough through the snorkel.

I agree, vacuum related. Vacuum lines mixed up; possible but I don't think so. I made a diagram and labeled them before I removed the lines. I couldn't find a diagram in the service manual. The breather was off of the TBI when it was dying, so lack of air is not the issue. Getting ready to take the TBI off again and double check it.

I logged onto your thread to see if you had discovered your problem. I was going to offer to send you a god TBI to try out.

Just sent you an email.

Thanx

Throttle body gasket needs replaced and the passages to the egr are partially clogged. I know when you may have replaced the egr it looked clear but that is not where the problem lies. Trust me we had this issue for a year until I discovered it on our 2.5

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1984 Indy Pace Car\1988 Formula Custom
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