Duck

Hello,

My wife was driving our 1990 C4 today and at stops the revs would be anywhere between 1200 to 2000. It would stay fairly constant and not fluctuate while at idle, however at one stop light it would be 1200 and the next it would be 2000. It has recent new caps, rotors and spark plugs. I have just installed a primary bypass as well. I have read on another thread that the O2 sensor can affect the idle. What other items would be good to check for this situation.

Thank you so much for all the help.

Michael

dboyle

One potential cause could be the idle air control valve (IACV or IAC). I am tracking down a similar high idle post warmup that I think is caused by a valve that just wants to stay open. Mine idles fine when cold for the most part but once warm wants to idle high.

You can search for cleaning tips, basically involves carb cleaner. I would include it but I don't have the number of posts to post links

Let us know what ends up curing it!

-Dave
______________
'91 Strosek C2 (supercharged)
'00 Honda S2000
'04 Honda Element (hey need a practical car for New Hampshire)

Naptown

mine car does the same thing. 89 C4. fine when it starts up but once warm the idle hunts from 600-1000rpm. car goes into the dealer next week. i'll post what they find, if anything...

CraigyB

I had this and it was very simple indeed..
When you aren't pressing the throttle, on top of the engine where the cable ends up, the throttle should be pressing the idle microswitch. Poor description, but it's pretty obvious when you lift the engine lid and look at the throttle. Just made an adjustment so that the switch was pressed, problem solved in 2 mins flat.

DaveK

A hunting idle is not the same as a constant high idle. There are a lot of threads on hunting idle - a search might save you some money. But I haven't seen many threads before about a constant high idle.

Andy Roe

Have you checked to see that the floor mat is not fouling the gas pedal?

Duck

Thanks for all the ideas. I will check out each and let you know what I discover.

Thanks again.

Duck

I went out and looked at the throttle mechanism in the engine compartment. I did find one switch however it is not close to being pressed. Is the idle switch?

Thanks.

drisin80

yes-- that is the idle microswitch. when the throttle (pedal) is released, that little bar should press the microswitch which controls the idle at 800 -900 rpms. what appears is happening--from your picture-- is that the throttle is in an open position when the accelerator pedal is not depressed. i looks like you need a cable adjustment so that this microswitch engages. ---- tom

JasonAndreas

Duck

I tried to figure out how to adjust the bar to meet the idle switch, however it is not straight forward. I tried adjusting the cable that comes across the front. It cannot been seen in the picture, but is off the bottom right corner of the picture. (I hope this makes sense.)

CraigyB

Were you successful ?

drisin80

hi-- there are two places to adjust the throttle. i adjusted mine at the pedal under the floorboards, and there is an adjustment where the cable goes through the body. do a search under "throttle adjustment", and you will find several helpful threads on this with pictures.----tom