krcrandall

Hello all,

I have done a search for this problem recently, and have not had much luck on my specific topic. I have put a new IAC on my 85 auto recently, which fixed a rough, inconstant idle. However now that my idle is fixed, when driving the car the idle wants to stick. If going 50mph for example and stop at a light, my idle will stick around 1400 until i give it one quick rev and it will drop back where it needs to be. I have heard this could be a vacuum leak which I plan on checking soon, however my mechanic said I would have idle problems at all times if this was a vacuum leak. I reset my idle after replacing IAC, cleaned throttle body, installed new fuel filter, and various other things not related to this problem. Is there a sensor that may be sticking? My thoughts are possibly I purchased a bad IAC which is sticking? Any help is greatly appreciated!

rodj

Is throttle cable and pedal free?
May be binding up and needs that tickle to let the TB close fully.

StealthLT4

There are 2 possibilities. Either your throttle cable is sticking/binding, or the throttle body shaft has worn the housing oblong. You can check which one it is by manually manipulating the throttle with your hand. Open it up all the way (engine off of course) and slowly close the throttle. If the cable binds before the throttle reaches the full-closed position, then its the cable. If the throttle binds and leaves slack in the cable, then its your throttle body.

If it's the cable, you just need to lube it up and check as much as you can for kinks.

If its the TB, you can either send it to a machine shop to have the holes overdrilled and bushings installed, or just buy a new/remanufactured TB. I faced this about a year ago, and got a TB on eBay that had bushings installed and bored to 52mm for about the same price as fixing mine would cost.

rich653

I had the same problem with my throttle sticking it was the throttle rod bushings, if you wiggle the throttle and there's any play at all the bushings are bad.

jeffp1167

I have a 90 firebird v-8 TBI that does this crap too. on cooler days it is very annoying but hotter days it never does it. Is this the same symtoms or am I dealing with something totally different.

when its cool it acts like my car has a sticking choke and when I quik snap the accelerator it idles down. I don't understand how a cooler day could affect the throttle bushings because this car does it even after driving it until it gets up to operating temperature.

I've often wondered if its a slow responding IAT sensor that isn't responding fast because my car has functional cold air induction through the hood.

my best friend has a 90 vette with a six speed and his car does the exact same thing. However he replaced his throttle body with a new one and suprisingly the car still does the same thing and the problem has never been found on his car.

So I was curious are your idling conditions more prominent on cooler days with you TPI's as well?

Crzyfrlss1

I was looking through AllData and found this idle adjust procedure.

Idle speed is speed is controlled by the ECM through the Idle Speed Control motor and is not adjustable. The minimum air rate is adjustable as follows.

1. Ground diagnostic terminal, turn ignition to on position.
2. Wait 45 seconds for IAC to fully seat, then with ignition still on disconnect IAC connector.
3. Remove ground from diagnostic terminal and start engine.
4. Adjust idle speed to specifications.
5. Turn ignition off and reconnect IAC connector.
6. Check TPS voltage, then start engine and check idle speed.





I won't be able to try it out until this weekend, but it should help some of you out with your idle problems.

krcrandall

Thanks for all the quick and helpful responses. Will check cable, pedal, and throttle body for sticking asap. I have reset the idle before, which did definately help after changing my IAC, so if your having problems with your idle try that.

My problem happens all the time.. the weather does not affect it the slightest.

I'll repost what I have found out in the next few days.

M.J.L.

Mine does the exact same thing.

krcrandall

So I found enough time to take a look at the problem this weekend. All cables are loose, the throttle gets stuck however. if you disconnect the cables, and manually rev the car while running, the throttle will get stuck. This does not happen while the car is off however. The throttle is smooth when not running. This leads me to believe that it must be some sort of sensor keeping the throttle partially open when the car is running? Any more help is appreciated.

floridamale

Check the TPS voltage should be .54 volts at idle
You might try leaning the TB there might be some build up on the back side of the butterfly or the shaft.