1994 Cherokee SE - Hi Idle Speed

[jmsummers]

My 94 Cherokee SE (inline 4) has been idling very fast lately. If I pull up to a stop sign or traffic light, the only way to bring engine speed down is to relax the clutch to the point where gears start to engage.

There has been a distinct "electrical" smell from under the hood and there is a high pitch chirping sound (not a whine) that causes me to believe the electronic switches for th injectors are just running at full tilt. I suspect the ignition control module is the culprit, however, my Chilton's manual talks about a Powertrain Control Module (which I can't locate on PartsAmerica's web site).

Am I on the right track with this?

Original engine has 190K+ miles. Plugs, wires, etc replaced 18 months ago. Oil changes at 3K - 5K miles regularly.

I appreciate any help.

[AlohaBra]

First thing to do is to open the hood and check all the linkage. Then take the air filter elbow off to inspect the throttle body. Also look for hoses that might be worn and pulling in more air.

Then with the hood still open run the engine and press on the throttle to see if you can see or hear something irregular.

Cleaning the throttle body at this point would be a good idea (inside and under the plate). Make sure you clean the shaft too.

[jmsummers]

Everyone needs a bath sometime... but cleaning the throttle alone didn't do the trick. Did notice that applying the carb cleaner to the block near where the fuel inlet manifold is bolted on I could duplicate the same effect as spraying the cleaner on the throttle body. That tells me what .. gasket problems? Seems like all the valve cover bolts could stand for some tightening too (a little bit of oil seepage).

What say you?

[AlohaBra]

Okay, How fast in rpm is the idle now?

At 190K, the intake gasket could have a leak. Which area, front or back? Tighten the valve cover or even reseal.

A way to check the intake (although messy) is to put engine oil in a squirt can and squirt it into the area that you think is leaking (with engine running) and see if you can hear a change in engine speed.

Also, check the IAC (idle air control) valve..

[jmsummers]

I don't have a tac in this Jeep. But I can tell you that on even pavement, I've noticed that I don't have to step on the gas pedal to accelerate; 35 - 42 MPH in 4th gear without any help from me!

I sprayed the carb cleaner alongside the valve cover just above the intake manifold from front to back. Hopefully that didn't cause any harm. From front to, I would say about center, the engine speed would change as a result. I spent the $30 for the little code reader book. I'm getting 2 different oxygen sensor codes indicating rich.