Hey folks, my 1999 stock xj is having some serious stalling issues. The check engine light has been on for a few weeks. i brought it into a jeep mechanic and he said he couldnt find any issues, but that this air valve (picture below) shouldnt be uncovered. He covered it with a rubber cap. A week later, im noticing strange behavior when at idle. the engine stuttering, but nothing beyond that. about a week later, it wont start up. the engine turns over and actually starts, and then stalls after a few seconds. after a few days of trouble shooting, I removed the rubber cap that he placed on that valve, and the engine started up right away. I left it on for about a minute, and when i shifted into reverse, it stalled again. Now it starts up no problem, but it will stall after about a minute or so while still in park. Sometimes I can shift no problem, other times I shift into drive or reverse, and boom,. it stalls again...What could this be?? also, what is that valve, and should it in fact be covered? when the engine is on if blows air out...

 

Find a new mechanic....

Did he bother to try to pull codes?

 

I would expect that spot to suck air in. I would also expect your mechanic to have access to service data that would explain to him what is supposed to be plugged in there so he could fix it rather than cap it.

 

I'm pretty sure that your particular year has a idle air control (IAC) valve that is located by the throttle body that would also cause stalling because of the little valve is stuck my either needs to be cleaned or replaced. Also clogged fuel injectors cause you to stall. Also faulty coil packs and faulty spark plug wires will also have you stall. And just recently I had to change my ignition switch which a faulty of those will also have you stall. You might need a new throttle body because a failing throttle body will have you stall as well. It may seem like a lot but those are some of the common reasons why your vehicle might be stalling. And every last one of these fixes that I mentioned you can do all yourself no mechanic required. Except for when you replace your throttle body you will need to get it programs or in other words the relearn process. Hopefully this helps

 

CRUISER'S MOSTLY RENIX TIPS

THROTTLE BODY AND IAC CLEANING

OCTOBER 30, 2015 SALAD 23 COMMENTS
Originally by TJWalker of CherokeeForum & JeepForum



The Idle Air Control (IAC) is mounted on the back of the throttle body (front for ’87-’90).

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 retracted, the air control passage flows more air which raises the idle speed. When the valve plunger is extended, 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. This should be part of a normal tune-up procedure and whenever idle/stalling issues are present.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

1. 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). On ’91 and later, it may be easier to just remove the whole throttle body. Be sure to use a new throttle body to manifold gasket when reinstalling.
2. “Gently” wiggle out the IAC from the throttle body. Gasket/O-ring on the IAC can be re-used if it is not damaged
3. 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 oxygen sensors. 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.
4. Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner.
5. It is also a good idea to clean the entire throttle body bore itself, the butterfly valve inside of the throttle body and it’s edges, and all associated linkage as long as you have things disassembled.

 

I'm pretty sure that port is supposed to be capped off, so the mechanic at least got that right. It would be nice to know what the check engine light code is.

 

I spent months chasing an intermittent stalling issue. In the end it wasn't a lesson in which part will fix my boo boo like a band aid, but more of overall Jeep philosophy,

The things that will cause a stall/no start condition in my experience:
1)Vacuum lines- go over them with a fine tooth comb. Not sure of the differences between your model and a Renix, but the MAP vac is major. This one alone was a huge catalyst in my stalling condition, but even the lines you think wont make a difference definitely do. Just fixed the HVAC vac line and it was noticeable so check them all. The stuttering you mentioned is really making me think you need to take a good look at the lines, their condition, and how they are routed.

2) Electrical- So this is broad as it covers sensors as well, but check ALL the wiring. Check for nicks and corrosion on the wires. Refresh your grounds. Funny story: One time I had a no start condition while on the road. The car would crank and crank. I got my hands under the hood while my wife cranked, and while doing so I had the **** shocked out of me. Turns out the wire from my ICM to dist cap had a crack in it and electricity was arcing off onto my lightly wet coolant overflow hose. A piece of electrical tape on the crack and I was good to drive to the parts store. This just shows you how random and unexpected it can be. Don't forget wire loom either- the wires on my TPS and IAC were exposed for a while, didn't think anything of it. Noticed it one day, thought it was crazy to have them exposed to manifold heat like that, put on high temp wire loom and BOOM, the jerkiness in my idle dropped about 90%.

Again. not sure of the differences between our models, but I'm sure Cruiser's tips apply in some areas so go through those.