High Idle

[TealZR1]

Fighting a high idle around 1100 when hot. Troubleshooting now replaced PCV Valve rubber and tightened up all hoses.
Saw where an easy troubleshoot would be to change the IAC Valve on top of plenum possible problem. Is this as easy as it looks? Could it be the issue?
Thanks to all in advance.

[Roadster]

Fighting a high idle around 1100 when hot. Troubleshooting now replaced PCV Valve rubber and tightened up all hoses.
Saw where an easy troubleshoot would be to change the IAC Valve on top of plenum possible problem. Is this as easy as it looks? Could it be the issue?
Thanks to all in advance.

Just had a similar issue with my 94 after the Plenum pull last weekend. Engine would sometimes idle at 1000-1000 rpm's and then sometimes at 800 rpm's. Ended up taking out the IAC and giving it a thorough cleaning. Had a lot of carbon build up on it. Replaced and all is good. Starts and revs up to 1500-1700 rpm's and comes right back down to 700 rpm's for a perfect idle. Also cleaned inside of the opening in the plenum/throttle body area where the IAC is seated. It is as easy as it looks......

[mike100]

It is probably one of the large vacuum lines under the plenum...the gas tanke purge system lines- they sometimes pop off if there is a backfire or some similar event.

[msuhanek]

Thanks roadster and Mike 100 for the quick reply. Those are my final two options. Will look at the IAC valve this weekend and pull the Plenum down the road if needed


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[mike100]

it has been talked about before (do a search), but if you take off the air duct and block the throttle body with a stiff piece of cardboard or a phone book (anybody still have one of those?) the engine should stall. if it still runs, you can clearly locate the vacuum leak noise under the plenum.

[BigIke]

My hunting and high idle was caused by the large vacuum line under the upper plenum. I zip tied the hose to the plenum nipple.

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[Roadster]

I stand corrected, just took the 94 out for a ride, and close to the same thing on the idle. Sometimes coming to a stop idling at 1000-1100 r's. Other times around 800-900r's. So it looks like cleaning the IAC really did not have any effect on the idle, at least for me.....

[secondchance]

I stand corrected, just took the 94 out for a ride, and close to the same thing on the idle. Sometimes coming to a stop idling at 1000-1100 r's. Other times around 8-900r's. So it looks like cleaning the IAC really did not have any effect on the idle, at least for me.....

Start by checking throttle body for possible binding. Also, check TPS voltage with throttle body closed.

[Roadster]

Start by checking throttle body for possible binding. Also, check TPS voltage with throttle body closed.

Copy that....will do.....

[lfalzarano]

Or you can send it to Marc! He fixed mine.


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