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Weird dead, low, high idle issues

roboter

NAXJA Forum User
Jeep was dying at idle once or twice every 3 or 4 days for about 3 weeks. From out of nowhere it now has high idle 1850rpm from cold engine start. Traced the TPS harness and swapped in a good TPS. No change, still idles high.
Any ideas?
 
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What year/engine? Always post that as there are significant differences through the years.

1. Clean throttle body and idle air control. They often get carboned up over time and miles and a good cleaning often restores full function. More on that below.

2. Know that a marginal battery can create "stalling". Load test the battery. Any parts store will do this for you for free.
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The Idle Air Control (IAC) is mounted on the back of the throttle body. The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

Reinstall IAC and check idle quality
 
My wifes 99 had similar similar symptons. I cleaned the TB etc and nothing changed. I then had the battery tested. And the battery was bad. Changed the battery and it is working fine now. Pretty much what BirchlakeXJ said.

Lil Joe
 
It's a 1992 with the 4.0 HO. Sorry for not stating that on my OP guys. :doh:
Been searching the forum and I'm assuming no adj is needed on the TPS. I exchanged it for another one and will attempt the tb cleaning. Thanks again, I greatly appreciate it.
 
I cleaned the IAC and throttle body. Now it idles about 400rpm higher. I notice that the IAC was loose in the throttle housing. I could twist it about half inch either way. It's been like that since I owned the Jeep and I'm assuming that ain't right.

Do I need to perform a reset on the computer or maybe a new IAC? :dunno:
 
I'd get a new idle air control in there. Cleaning "can" but does not always restore function. I don't think they are too expensive....

Let us know if this helps....
 
Well the Jeep is fixed. Bad IAC in conjunction with a dirty tb. TPS thrown in for added insurance. Thanks guys for your help and patience.

birchlakeXJ -
I owe you a case of brew dude!

:cheers:
:sunshine: NAXJA
 
Well the Jeep is fixed. Bad IAC in conjunction with a dirty tb. TPS thrown in for added insurance. Thanks guys for your help and patience.

birchlakeXJ -
I owe you a case of brew dude!

:cheers:
:sunshine: NAXJA

I will stop by Loomis California next weekend. HAVE THE BEER COLD!

Glad I could help......:wave:
 
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