• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

high idle problem on 89 4.0 what do i do????

blazinjames

NAXJA Forum User
I have a 89 jeep cherokee, 4l auto with 320kms on it and it has a high idle problem.

when i bought the jeep the previous owner had the Idle air control motor unpluged and i pluged it back in and the idle went very high, he told me he had that problem and eventually the idle would go back down and when it does i should unplug it and it will run fine. so i did that and it ran fine with normal idle for a couple years then i lent the jeep to my buddy and he was looking under the hood and pluged the IAC back in and now im having the same high idle problem.

but now it will not go back down and it just staying high

i want to fix the problem but im not sure what to do? is it for the the IAC that is the problem or could it be something else?

should i just buy a a new IAC?

im new to doing anything having to do with electronics on a vehical but i would like to figure out how to trouble shoot this problem. can i figure out what is causing the high idle with a multimeter? if so what setting and what am i looking for??

Thanks
 
I would pull the IAC and clean it, and clean the throttle body while you are at it. Use throttle body approved cleaner, not carb cleaner. Use a stiff toothbrush and Q-tips on the IAC, but be gentle with it as they can break.

While you are in there, check the base idle screw setting--it should just barely start to open the throttle plate. Its job is more to keep the throttle plate from slamming closed than setting the idle.
 
Could be. Or any loose vacuum bleed that was never found and fixed - vac tubes, hoses, manifold bolts, bad intake gasket, throttle body gasket or bolts, etc etc. Not to forget the entire vac system for the heater or a axle disconnect, right down the football or can, where ever it may be hidden.

X2 the screw, it's just a throttle stop, not an adjustment. Spraying all the joints, connections, seams, and stuff with a can of carb cleaner and the little tube will help to discover it.

Have fun with that!
 
I would pull the IAC and clean it, and clean the throttle body while you are at it. Use throttle body approved cleaner, not carb cleaner. Use a stiff toothbrush and Q-tips on the IAC, but be gentle with it as they can break.

While you are in there, check the base idle screw setting--it should just barely start to open the throttle plate. Its job is more to keep the throttle plate from slamming closed than setting the idle.

I second this.

We had one with same problem. Cleaned IAC and problem fixed. They get all gunked up.
 
i cleaned out the IAC and it still is idling high. with the intake off of the throttle body while it was idling i cut off some of the air getting sucked in and it was idling alot lower..
 
Did you check the "base idle" screw???

It was probably cranked up by PO when the IAC stopped working.
 
Pull off the intake tube, observe the throttle plate.

On the side of the throttle body is a little boss with a 3/32 allen screw in it that acts on the throttle shaft linkage.

Back it out so that the throttle plate is fully closed and the allen screw is not in contact with the shaft's linkage, then turn it in so that it JUST starts to move the throttle plate.
 
Back
Top