Finally broke down and bought a smoke test machine. I got it hooked up and the only places I had smoke appear are from the EGR valve itself (not the tube) and from both ends of the throttle plate shaft holes.

Since the engine is not running would it make sense that smoke would escape from the EGR valve? Also is the leakage at the throttle plate shaft holes expected? Are there seals in the TB for the shaft?

quote Originally posted by ketstang: Finally broke down and bought a smoke test machine. I got it hooked up and the only places I had smoke appear are from the EGR valve itself (not the tube) and from both ends of the throttle plate shaft holes. Since the engine is not running would it make sense that smoke would escape from the EGR valve? Also is the leakage at the throttle plate shaft holes expected? Are there seals in the TB for the shaft?

There is a rubber diaphragm inside the lower (underside) portion of the EGR valve that you can touch when cold, that ... when vacuum is applied from the engine, either opens or closes the EGR valve (I forget which). The EGR valve gets vacuum directly from the intake plenum, so in this case ... if you are getting smoke from the smoke test coming out of it, then that's an indication that the diaphragm is damaged and there's a leak there. Replacing the EGR valve would solve this.

I'm not sure I'd really be too concerned about smoke escaping from the throttle plate shafts though... I'd almost expect it a little bit. You could probably grease them a little if you were concerned.





I'd never thought of doing a smoke test... that's actually pretty awesome. What is it that you are testing for... vacuum leaks? What symptoms are you having that made you decide to test this (I might have missed a prior thread)? Also... what did you use to conduct the smoke test? I'd never even heard of that outside of sealing up a house... would love to know what kit you used... I can tell how this would be hugely valuable.

Also, vacuum runs along the underside of the engine to the front compartment's brake booster. If you didn't already check, you may also want to see if any smoke is coming out under the tube that runs under the car to the brake booster, and the brake booster itself.

[This message has been edited by 82-T/A [At Work] (edited 09-20-2023).]

I believe 'ketstang' is still working on this thread:

High idle problem, unable to solve. by ketstang
Started on 07-07-2023
https://www.fiero.nl/forum/Forum2/HTML/147013.html

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

TB/TBI/Carb do not seal the throttle shaft & even new units can "leak" there & more like thru IAC path & throttle butterfly.
Worn TB/TBI body then shaft can cause bigger leaks but engine doesn't use MAF so ECM etc won't care. Nor many small vac leaks on other lines/parts as long as can adjust IAC to make up for the leak. O2 sensor is only thing to tell have enough air to mix w/ fuel.

PB booster & line can leak but hard to see.
Most of the line is hidden.
Booster can leak internally & hard to see only outlet via pedal or MC push rods.

Is why careful discon or pinch that line @ engine & plug engine side looking for leak problems.
Pinch line maybe hard w/ short or hard rubber line sections. Short sections tear @ edges of metal lines when pinch. Old Rubber gets hard & pinching won't seal.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

quote Originally posted by Vintage-Nut: I believe 'ketstang' is still working on this thread: High idle problem, unable to solve. by ketstang Started on 07-07-2023 https://www.fiero.nl/forum/Forum2/HTML/147013.html

Yes, I am still trying to figure out why I have a high idle problem. I've been messing with this problem off and on for months now. It's my brother's car and thankfully he wasn't in a hurry to get it back.

Someone suggested doing a smoke test and I watched a YouTube video where a guy tried using a cigar and blowing the smoke into the brake booster port. I couldn't see any leaks that way and I'm not a smoker, so I didn't try too hard. I broke down and bought an inexpensive (<$65> "smoke tester" on Amz and it actually works great for making smoke. After blocking off the TB intake with the balloon attachment they provided, I hooked the machine up to the hose and started looking for smoke. Other than the smoke coming from the places I mentioned earlier in this thread, I found no other leaks. I forgot to look for possible leaks in the brake booster line or the booster itself. I'll do that next time I'm in the shop.

So maybe my problem is a leak in the EGR valve itself?

quote theogre: PB booster & line can leak but hard to see. Most of the line is hidden.

When I checked my brake booster vacuum line:

*Disconnect both ends of the vacuum line from the brake booster and the plenum/manifold.

*Cap/Seal the vacuum line at the booster end.

*Attached a hand operated vacuum pump with a gauge at the plenum/manifold end.

*Draw-out the atmospheric pressure to 20 inch-Hg

*Hold the pressure for 5 minutes.

IF your brake booster vacuum line won't hold pressure......you're now looking for leaks.

[This message has been edited by Vintage-Nut (edited 09-20-2023).]

Great idea! Thanks. That's kind of how I tested all the lines in the engine bay.

quote Originally posted by Vintage-Nut: When I checked my brake booster vacuum line: *Disconnect both end of the vacuum line from the brake booster and the plenum/manifold. *Cap/Seal the vacuum line at the booster end. *Attached a hand operated vacuum pump with a gauge at the plenum/manifold end. *Draw-out the atmospheric pressure to 20 inch-Hg *Hold the pressure for 5 minutes. IF your brake booster vacuum line won't hold pressure......you're now looking for leaks.

And you replaced GM 25036979 Sensor, engine coolant temperature for the ECM- yes?

Edit

A Tip when you check the brake booster vacuum line
and
IF your brake booster vacuum line will hold pressure:

*Keep the cap/seal on the vacuum line at the booster end
*Connect the vacuum line to the plenum/manifold
*Run the engine - the high idle problem is still here or gone?

IF Still Here - I bet that the booster is 'okay', but keep the cap/seal on the vacuum line at the booster end as you troubleshoot.
IF Gone - Check the Booster Check Valve Gasket and as Ogre said it may be leaking internally.

*Edit Two - Brake Booster 'Health' Clue*

When I replaced the Booster Check Valve & Rubber Gasket, I heard the confined vacuum in the Booster ESCAPE.

*If you're wondering about the 'health' of your Booster; one test is to charge the booster vacuum, and then allow it to sit overnight. The next day, remove the Check Valve and listen for escaping vacuum....No sound is a bad sign!

[This message has been edited by Vintage-Nut (edited 09-21-2023).]

Yes, I replaced that sensor over the past weekend.

quote Originally posted by Vintage-Nut: And you replaced GM 25036979 Sensor, engine coolant temperature for the ECM- yes? Edit A Tip when you check the brake booster vacuum line and IF your brake booster vacuum line will hold pressure: *Keep the cap/seal on the vacuum line at the booster end *Connect the vacuum line to the plenum/manifold *Run the engine - the high idle problem is still here or gone? IF Still Here - I bet that the booster is 'okay', but keep the cap/seal on the vacuum line at the booster end as you troubleshoot. IF Gone - Check the Booster Check Valve Gasket and as Ogre said it maybe leaking internally.

Hey 'ketstang' - did you got your high idle problem solved or.......?

I replaced the engine coolant temperature 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 everyone!

quote Originally posted by Vintage-Nut: Hey 'ketstang' - did you got your high idle problem solved or.......?