JoMamma_Smurf

Hello.. First post. Searched a ton on many forums and still haven't fixed my issue.

Ok.. here goes. 94 Cherokee country 4.0 automatic 2WD. Idles between 1500-2000 rpms when in park, drops to about 1100 when in gear and driving. I've done sooo much to try and fix this. It started happening kind of suddenly. Happens all the time. Here is a list of things I've replaced:

I've replaced every vacuum line I could find that was even questionable. Found one from the fuel tank that was just rotted. Replaced it but have no clue where it goes under the hood.

Brake booster had big leak.. I thought this was my culprit but didn't help much at all when I replaced it. Brakes are better-ish but not great. Seems no matter how much I gravity bleed it the front calipers seem to have air in them. Maybe master cylinder??

Replaced TPS and IAC.

Removed and cleaned throttle.

Replaced PCV and CCV valves and grommets.

Only thing I could add that I don't know if it matters or not is that the controls on the AC blower speed stopped working and it only blows on the high setting.

I'm stumped at this point and need help. Sorry for the long post. I wanted to be thorough.

EDIT: Just wanted to add that the temp gauge never worked. Don't think it's related. I just never got around to replacing the temp sensor.

steelybill

I suppose it's possible that the intake manifold could have a gasket leaking air, or the throttle body base gasket leaking air.
Is the throttle arm all the way down on idle speed position ?

JoMamma_Smurf

Yes. I backed out that screw all the way and replaced the gasket for the throttle when I cleaned it. I sprayed throttle cleaner all over the place to try and detect a leak but didn't find anything. I even torqued all the intake bolt to see if any were loose. Not totally ruling out the intake gasket but who knows.

Could the channels in the valve cover for the CCV and PCV valves be super clogged causing this? I tried to clean them as best I could when I had the valves out but they were pretty dirty. I may remove it and clean it.

drhoward1988

I don't know much about the H.O. motors(renix owner) but check into TPS adjustment. I know on the older renix models if the tps isn't set correctly it'll cause idle problems.

steelybill

According to the Service Manual, with the engine at operating temp, at idle the PCM gets inputs from CPS (crank) and CPS (camshaft) sensors, engine coolant temp sensor, MAP sensor, TPS, and oxygen sensor., and also adjusts idle speed through the IAC

Maybe some of this info will help....

xjforlife

This may be a bit of a longshot but my buddys YJ was having a similar problem a few years back it ended up being an oxygen sensor

Firehawk068

Wow, you got alot going on there!

First of all, gravity-bleeding your brakes will not remove air from the lines.
The fluid will not be moving fast enough to flush the air bubbles out, and they will just continue to rise up and congregate at the highest point.
You need to get the fluid moving faster by pressure-bleeding, or vacuum-bleeding all 4 wheels.

The blower motor only working on high, is usually the blower motor resister has failed. They are relatively easy to replace, and relatively inexpensive.($10-$15)

The temp gauge on the dash uses the small, single-wire temp sensor that is on the back of the cylinder head, on the driver side. The gauge is the only thing it controls.
The computer uses the 2-wire sensor that's mounted to the thermostat housing on the front of the engine.


The idle speed issue could be a little more complicated. It could be a vacuum leak, or it could simply be the idle air control valve not working properly.
It would have to be a fairly large vacuum leak to affect the idle speed that drastically, and would be fairly easy to find. (like a hose disconnected or broken off) You could rule out the intake/exhaust gasket, or other source by spraying starting-fluid all around the intake, top and bottom where it meets the head. Also anywhere there is a vacuum junction.
You can rule out the brake booster by disconnecting the large hose and plugging the end with your finger. (does the idle return to normal?)

If none of this fixes it, than it is most likely a throttle body issue.
Does the throttle plate close all the way?
You stated you backed the screw all the way. (normally this is pre-set from the factory, and never needs any adjustment) If the throttle stop bracket is bent somehow this could be your issue.
You mentioned that you also replaced the IAC? Make sure the electrical connector looks clean, and all the pins make contact. This is how the computer adjusts idle speed.
You might remove the IAC and take a close look inside (where the cone shaped valve meets the idle air hole) make sure there is no carbon or bits of debris stuck in there. (don't pull on the cone or attempt to unscrew it. )
Also make sure the o-ring is intact on the IAC and it is seated properly.
Could also be a defective IAC, or possibly the wrong one? It could happen.

If none of this results in a fix for your issue, a last result would be to hook up a scanner that you can monitor live sensor data with.
Check to see what the computer thinks the engine speed actually is?
You might see something like:
-Engine RPM
-Idle Speed Request RPM

You could also use this to check TPS operation (this can also be tested with a volt meter) and other sensor data like Oxygen, and temp sensor.

Anyway, hope this helps, and you get it sorted out.

JoMamma_Smurf

Thanks a lot for all the input!!! I can tell you that there is a strait pipe welded in where the cat was. This vehicle only has one o2 sensor behind where the cat should be. I've also been able to trigger a CEL if I unplug some of the vacuum lines but it goes away when I reconnect it and restart it.

I'll look into the crank and cam sensors.

I'm going to smoke test it to finally rule out the possible vacuum leak. It may very well be the throttle. I may pick up a throttle from the JY this weekend just to try it..

freegdr

Have you checked for codes yet ?

JoMamma_Smurf

No. I don't have a code reader

Turbo X_J

OBD1 doesn't require one, search "key test".

xjforlife

What's you said there's so cat the o2 sensor behind were the cat should be is picking up weird readings and its causing it to run rich try putting a high flow cat on and put the o2 sensor in behind it while your at it replace both of the sensors on the exahust

freegdr

Dont need 1 .....

http://jeep-xj.info/HowtoECUcodes.htm

JoMamma_Smurf

That is awesome. I'm going to be doing this tonight.

JoMamma_Smurf

Checked for faults. Got 55