Okay, so when I start my XJ, it Idles very rough and doggy. But after It runs for a bit it settles out. I went to autozone to grab my U-joints today and it happened so I asked about it and the guy said it may be the fuel pressure or the fuel filter/pump. Anyone have any idle issues or running problems like this?

 

Welcome to the forum!

It is handy for the forum to know, what kind of XJ you have, so mention year, engine etc. Even better, fill in the personal info etc and you have to only do that once.

Rough idle is quite a common issue. If you do search on here, you will come up with quite some ideas, so give that a try.

Besides rough idle, any issues when driving? And once all warmed up at idle, so stopped for let's say a traffic light, any rough idle then? Or only when it was parked for a while?

Just some ideas: if it's just the rough idle, cleaning throttle body/valve and the Idle Air Control (IAC), would be good first steps. If it's a rough idle every time is has been sitting for some time, cold or warm, leaking fuel injectors could be in play, etc. etc. These are just three of the items that could be involved. But not the only ones...

 

Well I have a 2000 2 door xj sport, 4.0, 4x4, and the rough idle seems to go away the come back after driving somewhere then parking, even if for a minute. And the oil pressure drops to maybe 25 or so. And when it's running in that conditions the throttle is somewhat unresponsive and times, and the jeep seems to bog itself down... I've tried the seafoam in the gas so far... Just kinda lost now

 

So only after the engine was shut off and started up again it idles rough and clear out, no issues when idling in front of traffic light?

 

Thats the thing, it could be just at start up, sometimes at the red like, sometimes it last until i hit the highway. If you've ever driven with a cylinder down that's what it seems like...

 

Those are known to boil fuel at times. Under the hood it's so compact that the jeep is prone to vapor lock. Usually this happens under the right conditions upon restart. My 2000 does this.

 

If you have not already done so, would check the fuel pressure. Easy check right on the fuel rail, can rule out a lot right there. That's probably the first check I would do if it were mine. Just to ensure it wasn't something as simple as pump, filter, or fuel pressure regulator.

 

Next time it's running horrid on restart pop the hood hand push the bleeder on the fuel rail. Usually if it's vapor lock air will come out as well as fuel.

 

I'd start with cleaning the throttle body and IAC.

Courtesy of TJWalker:
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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 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