Replaced IAC - now super high idle (Page 1/2)
Kitskaboodle NOV 21, 09:27 PM
Hi all, I replaced my IAC today because I have been having an occasional high idle issue and I suspected the IAC. It would idle in Drive at about 1300-1400 and 1800+ in neutral. It would go away after a while and idle as normal. (About 1000 rpm in drive) So...I decided to put in a new one, thinking that it was sticking, flaky, etc.
Along with replacing the IAC I sprayed carburetor cleaner in the IAC hole and throttle body. Once I got it started it is now trying to idle much higher, about 1800-1900 in drive and 2400+ in nuetral. First, I verified that the throttle body is fully closed (it was), then I unplugged the connector to the IAC and the idle went even higher. Out of desperation I disconnected the battery for 6-7 minutes but absolutely no change. The car is almost undriveable now. I’m worried I will break the trans so it is sitting for now. It’s an 85 GT Auto
Suggestions on how to get the idle down? Car was (to my embarrassment) running fine before I touched it today.
Thanks, Kit
LornesGT NOV 21, 10:44 PM
Place a paper clip in the ALDL terminals A&B to put it in diagnostic mode just like you would do for setting timing. Turn the key to RUN and wait about 30 seconds. As said above, you will hear it making noise as the ECM is commanding the IAC fully closed. After 30 seconds pull the IAC power connector while the key is still in RUN. Now you turn the key to OFF, remove the paper clip and reconnect the IAC. Now drive the car over 35mph to relearn idle.
Patrick NOV 21, 11:04 PM

If the engine doesn't stall with your finger covering the IAC port (and throttle closed), you've got a massive vacuum leak.
Kitskaboodle NOV 21, 11:20 PM
Thanks guys. I will try to check your suggestions tomorrow evening.
Forgot to ask a very important question:
Is it necessary to adjust the Pintle for Fiero V6?
I don’t recall doing it before. Kit
Dennis LaGrua NOV 22, 02:50 AM

quote
Originally posted by Kitskaboodle:

Thanks guys. I will try to check your suggestions tomorrow evening.
Forgot to ask a very important question:
Is it necessary to adjust the Pintle for Fiero V6?
I don’t recall doing it before. Kit



On some aftermarket IAC valves an adjustment of the pintle is necessary. On those the pintle screws in and out to determine the exact length needed to place it in neutral position before installing. IIRC you energize it on the bench and then you set the length of the pintle. The high idle may not be the fault of the IAC though. Much of the time a vacuum leak coming from a broken EGR tube is the problem.

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" 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 "

Kitskaboodle NOV 22, 09:02 AM
A broken egr tube and even a vacuum leak is unlikely since the extremely high idle showed up directly after I replaced the IAC and Gumouted the throttle body.
Kit
Gall757 NOV 22, 09:22 AM

quote
Originally posted by Kitskaboodle:

A broken egr tube and even a vacuum leak is unlikely since the extremely high idle showed up directly after I replaced the IAC and Gumouted the throttle body.
Kit



It's extremely likely since you were in there moving things around. Check the tube at the bottom of the throttle body that goes to the intake.
Kitskaboodle NOV 22, 11:54 AM
Woo-Hoo!
Thank you to all.
LornesGT instructions did the job.
I will have to say that I was a little worried because after I followed the ALDL jumpering sequence to reset the IAC, it still idled very high when I restarted the car. It was only after I drove the car on the freeway for about 5-7 miles that the car started to idle normally when I put it in nuetral. By the time I got home it was back to normal. As an FYI it idles at 900 in Drive and just a little over 1000 in Park/Nuetral.
Thanks again for all the replies.
Kit
fierogt28 NOV 23, 12:06 AM

quote
Originally posted by LornesGT:

Place a paper clip in the ALDL terminals A&B to put it in diagnostic mode just like you would do for setting timing. Turn the key to RUN and wait about 30 seconds. As said above, you will hear it making noise as the ECM is commanding the IAC fully closed. After 30 seconds pull the IAC power connector while the key is still in RUN. Now you turn the key to OFF, remove the paper clip and reconnect the IAC. Now drive the car over 35mph to relearn idle.





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fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.

fierofool NOV 23, 08:33 AM
Sometimes new IAC's can be damaged upon installation if the pintle is extended more than 1 1/8 inch as measured from the shoulder where the gasket sits. They should be pre-adjusted before installation or they can bottom out on the seat and damage the internals of the IAC.

There are two designs of IAC's. There are other methods of distinguishing but they can be easily identified by looking at the stem that the pintle is mounted on. One style has a smooth stem and the other has a slot running the length. Each one requires a different method of manual adjustment. The slotted stem requires pressing on the end of the pintle while moving it side to side. The pintle will slowly retract into the base. If you try to rotate the pintle and stem, you can break the tabs that fit into the slots on the stem. The second style with the smooth stem requires retracting the spring away from the pintle head and holding it. With this done, the pintle can be screwed back into the base.

Once the pintle is adjusted to less than 1 1/8 inch, it can be installed without damage and use the procedure LornesGT provided.

[This message has been edited by fierofool (edited 11-23-2020).]