geeknik

Hi all. I am having a problem with my engine dying. It happens usually when I'm braking, but not every time I brake. Freeway driving it's ok and most street driving as well. It starts up fine and shuts off fine. It started doing this Monday. I was able to pass my emissions today, regardless, just needed a new gas cap. I then put in one of them bottles of Lucas injector cleaner, the one Autozone tries selling you while you're checking out. I did the Lucas thing thinking it might help clean the injectors, but the engine is still dying at times. Later I went to my local Pull Apart and got that ceramic electric thing that's on the front of the driver side engine bay, near the air cleaner box mounted above the wheel well. Mine was cracked in 2. This one is solid. Later as I'm driving, the engine died, and then less than a mile later the rpm's are over 1000 just cruising, no pedal. I shifted to neutral and the rpms jumped to 2000+, no pedal. I got off the road and pulled one of the wires to that ceramic thing and the engine died. Started her back up, engine idling at 2000+ rpm, and tried the other wire, and it died. I pulled the wire harness from the yellow box under the dash on driver's side, I think that's the brain, maybe not. Started her back up and she idled fine.

Overall she drives good. Just this occasional engine dying and then high idle later on. Sorry for the length but I wanted to give as much info as possible. Does anyone have an idea what might be going on? I changed my plugs, wires, cap and rotor about a month ago, so I doubt that's an issue. Any ideas are appreciated.

ALLABOUTXJ

Use sea foam
As directed but first change your fuel filter

tjwalker

Your erratic rpms and stalling can be caused by a dirty idle air control and throttle body. Try cleaning it as this often resolves the problem. More on that below.

If cleaning the TB and IAC doesn't resolve, test and adjust your "throttle position sensor". It is the next thing to suspect after a thorough cleaning of the IAC and throttle body. You will need a meter and a manual to do this (analog meter best).

BTW, the resistor you replaced is the "ballast resistor" which is designed strictly to reduce noise on the fuel pump circuit. Being in-line, the fuel pump won't run when you pull a wires from it. If you have a new resistor, you should be good there so don't worry about that.
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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

geeknik

I will try this. Thank you.

geeknik

I did what you suggested, tjwalker, and it worked. I bought a can of Seafoam spray, because Autozone didnt have anthibg that said "Throttle Body" cleaner, thought there were a dozen brands for Carb Cleaner. Anyway, pulled apart the throttle bost housing and looked at the valve. Sure enuff it was gunked up. Opening the valve I saw there was a nice layer of gunk below the valve. Pulling off the IAC I saw it was covered in gunk as well. I Cleaned everything I could, including the inside housing of the air cleaner where the tube from the valve cover. Anyway, got it all cleaned best I could, buttoned it all back up. Initial start died. Tried again and the rpm's peaked at 1000 for a second, then settled down, followed by a nice plume of blue smoke from the exhaust. Took it for a drive down the freeway to clean out any residual loose gunk and Seafoam. Was perfect. Street driving is great! No hesitation on starts from lights. So it seems good now. One last question, what can one do to prevent all that gunk building up? Maybe some fuel additive, Seafoam maybe? Anyway, thanks for you help.

tjwalker

Glad I could help. The problem is so common that I have the above information in a "cut and paste" document, just waiting for the next guy.

As for preventing it, really not much you can do. It takes quite a few miles to get that carbon buildup. You can clean everything again if/when it acts up. Hard to predict.