idles at 2k

bought a 88 Cherokee 5 speed from a buddy about a week and a half ago.

today it started idling at 2 grand and would not idle down.
and overheated.

the motor was rebuilt 20k ago
has a throttle body spacer.

nothing has changed other than a new radiator hose that was split and leaking.

Could this be caused by a bad TPS?

i got it home and let it sit for a couple hours then drove it around the block and it was idling fine. any ideas would be great

Thanks,
Mitch

Check the TPS, vacuum leaks and the IAC can be sticking also. If its acting up try and tap the IAC and see if it goes away. You can also test the TPS and check for vauum leaks. There should be lots of decent write ups on TPS and IAC testing, if you can't find any I'm sure me or some one else can post up some good info. Make sure the cooling system doesn't have air trapped in it either.

i made sure there was no air in the system. what is IAC? sorry acronyms aren't my thing

Idle Air Control, its a four wire connector on the body. Its a little stepper motor and some times they stick, causing the idle to stay high or low or not change when needed. What I like to do is when the problem is acting up tap on it with something like the handle of a screw driver or a combination wrench and see if it unsticks and the idle will drop. There are other ways of testing it and checking the wiring also. The TPS can cause idle problems too.

You may also want to check to see if you have an intake manifold leak. Check to make sure the throttle plate is closing completely. Also check the EGR assembly. When I bought my '89 XJ the EGR valve actuator was rusted through and my Jeep idled @ 2000 RPM. My problem was a combination of bad EGR, incomplete closing of the throttle plate, and a malfunctioning IAC. Make sure your ground points are clean and tight. Renix Jeeps (1987-1990 4.0L) are very ground sensitive and proper grounds are important. You should definately remove the IAC and clean the piston and throttle body passages with throttle body cleaner.

All of the above, especially the EGR system.

Also, read this: http://naxja.org/forum/showthread.php?t=905849

Thanks for all the informaton i will have to try messing with everything after i fix a leak at the water pump. when it overheated on my way home it started leaking alot of coolant. my friend sayed it was from the weep hole but it looks like its coming from between the water pump and the block. so i am going to be replacing that gasket soon. it has stopped idling at 2k. and i am going to replace the TPS and IAC also.

What is the motor supposed to idle at? sometimes it will idle less than 500 near 250 and want to die and some days it will idle at 750 other days it will idle at 1k

Thanks,
Mitch

The correct idle for the 4.0 in the XJ is 700-750 rpm, after 20 minutes of operation.

That idle is maintained by the ECU/PCM solely by sending extend/retract signals to the stepper motor that is called the IAC--Idle Air Controller. Fortunately, IAC can be tested or exercised--unfortunately, it requires a dealer only tool to do it. Fortunately, they seldom fail; unfortunately, they become "lazy" with age.

Your TPS can be tested AND adjusted (91+ only tested).

Everything you will ever need to know about Renix sensors--please bookmark the page: http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

Chinese philosopher Confucius say: "Man that throws parts at problem seldom smiles."

joe_peters said:

That idle is maintained by the ECU/PCM solely by sending extend/retract signals to the stepper motor that is called the IAC--Idle Air Controller.

Click to expand...

Is there a published tables of voltages that the computer will push to the IAC? In other words, how can I verify that the signals going to the IAC are not jacked up?