BillDurant

I have a 1989 C-4 after some engine work it runs great but it idles high when at a light or stopped
I tap on the gas peddle and idle goes back to normal

I'm no mechanic but seems to me it's not electrical but something sticking ? needs to be lubricated ?

C4Coupe

Sounds like throttle body needs cleaned. For a "quicky" clean I use toothbrush, clean rag, and throttle body cleaner. Gets rid of carbon build up around the butterfly.

BillDurant

Sounds like a plan
thanks so much

aklim

Sounds like it's time to take the TB off, do the coolant bypass and clean the TB. Take the top plate off, take the IAC and the IAC housing off and clean all passages. Reinstall with fresh gaskets and see what the IAC counts are with a scanner.

I would get the engine to stable operating temp and turn everything but the motor off. Check what the CTS is saying with the scanner. Make sure it is right with an infra red thermometer. See what the IAT sensor says the same way. If both are right, rev the motor and see what the IAC counts are. Should be around 20-30. If it is higher, you turn the adjustment screw in. Rev and recheck. Too low, turn the screw out. If you can't turn anymore, you have an air leak somewhere.

gerardvg

Hi

First check the accelerator cable and cruise control cable move freely,
remove the clip holding them to the throttle body.
Check they move freely, also check the outer sheath at cruise control.
Connect both back to throttle body and move the throttle body open / closed, make sure the outer sheath does not pop out of the recess it sits in. If it does crimp that so its secure.

Has happened to me before I floor the pedal, the outer cruise control cable sheath would pop out and would not go back in every time.

aklim

TPS voltage should tell you that it is or is not hanging up.