xjcherokee90

OK I HAVE A 90 CHEROKEE XJ WITH 4.0 AND AUTOMATIC. WHEN I START IT UP(HOT OR COLD) i have a very high idle then drops back to normal. this happens every time. also after it warms up a lil when i start slowing down coming to a stop the idle drops and it stalls out. fires right back up. also after warm up it has rough idle but if it sits a few mins not under a load idle goes back to normal with a slight roughness to it. so i have put a new throttle position and a new idle air valve on and it is still happening. also my emmision main light is on. i have tried disconnecting the battery to reset but it dont turn the light off. was i on the right track or i have replaced stuff for no reason? what else could it be? also how would i go about adjusting the throttle position? i noticed i could turn it one way or the other a lil but how do i go about getting it set right as far as trial and error goes, cause so far nothing is working. all help is much appreciated in advance

xjcherokee90

wow, no reply at all?

The Rooster

How many miles are on it? when was the last time you did a tune up? are all your grounds clean?

freegdr

the only way to get the light out on renix is to remove the module its under the dashhttp://jeep.zerok.ru/index.php?page=144

speedballin

Uhmm maybe vacuum lines I had a relatively similar problem with idle changed Iac n nothin but throttle position sensor fixed it and pretty sure the rotation of the TPS is just changing rpm around I think lol. But vac lines might be one of the things u should check

The Rooster

or i would check this also...
Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 11-28-2011

cruiser54

Do what Rooster says first.

Then clean the throttle body.

Did you adjust the new TPS you installed?

armymedic120

Hey I've had problems with my headlights being dim, not being able to run windshield wipers and lights at the same time. I looked things over on the suggestions rooster gave and found my braided cable to be completely corroded away. Any suggestion on a temporary replacement?

cruiser54

Read post #6 towards the end. A Napa part number is provided. Why not read the whole thing, fix it all, and get this all behind you?

armymedic120

Man I would love to be able to, but I've already spent a small fortune trying to get this to run right, and seeing I don't have a very big income, it's a little frustrating sometimes.

armymedic120

Hopefully I'll get this full time firefighting job and make enough money to do things right haha

cruiser54

$20 if you do it all. $0 if you just refresh all the grounds taking less than 1 hour. Just do it.

crbnfibr

all you need is a socket set and a wire brush, you dont have to recrimp or rewire unless they are in "bad" condition... good luck w/ the job

xjcherokee90

my 90 model has just turned 150,000. motor was rebuilt not too long before i got it ans all vac lines and ground wires got replaced. traded with my buddy who said everything worked great till he pulled the iac and tps to clean them. then right after he cleaned started it up and all this started. first thing i asked was why fix what was not broke. i figured would be an easy fix, just replace the two things he messed with. so if emm main. light came on would it be a safe bet oxygen sen. went out? and what does the control mod look like under the dash that i need to unplug? sorry for my ignorance toward this but this is my first jeep.

armymedic120

Haha my 89 just hit 367,000