Anybody run into this.....

[Judd W. VA]

On my '98 XJ 4.0 w/85k miles occasionally the idle will become elevated varying from just over normal to 1000 to as much as 1200 RPM. I find this very anoying esp when dealing with stop and go traffic. It seems to lope when doing this because is not supposed to be this level of an idle. Other times will be perfect for a while.

Yesterday it was particularly bad and i taped on the ISC and went back to a perfect idle. I had suspected the ISC motor was hanging up occasionally causing this problem. Has anyone else dealt with this and how was it repaired? I am thinking i need to remove the ISC and clean it out- probably fowled with carbon. Those tamper resistant torx used to attach appear difficult. I think i have the tool for that.....

Thanks

 

[martin]

I had the same problem on my 86 ford mustang with the 302/5.0 engine. My mustang was the first year of fuel injection and I sold it in 1999 with 154,000 on it. Still ran great but 3 vehicles was too much for a bachelor - mustang, XJ and a Buick Century. Got the XJ and the Century from Dad's estate.

Anyway back to the topic at hand. I would experience similar things with my mustang the idle would swing 100, 300, 800 rpm from idle. My solution was to have the throttle body cleaned every 30,000 miles. I had a mechanic tell me "dirty idle air controller" caused my problem.

I recommend you have the throttle body cleaned then get on a regular schedule of cleaning. You also may want to look at where you buy your fuel, the addatives or lack of them can cause deposits. With the Crancase vent dumping into the intake it is possible for those gasses to get to the throttle body over time, especially on shut down.

When the mechanic cleaned my XJ's throttle body there was a layer of junk on the back side of the butterfly. I had to go back 18 months later to have it cleaned again because of the combutions products the stuck ERG was sending through the intake.

It just routine maintenance.

 

[XJ-ARMOR]

Invest in a whole set of torx.....they are essential to a do-it-yourself jeeper. I've experienced the same problem after i hydrolocked my motor. Idle was erratic. If a good cleaning does not help...then its the motor most likely.

 

[CharlesS]

Judd,

I had the same problem some time back....
Suggest you remove the throttlebody, take the TPS, IAC off the throttlebody and spray out the throttlebody and all ports with throttlebody cleaner. The seat and disc of the IAC can be spray out too.
This cured my problem.
A good set of torques bit screw drivers and 1/4" drive sockets can be purchased from SEARS.

Charles

 

[Judd W. VA]

Charles,

Good to hear from you. Been a while. Hope things are going well.

Yes, i surmized the problem was in the throttle body and associated valves. Could be the T/B throttle plate gets some gum around it and effectively closes the gap to a degree. In turn this causes the IAC or ISC to run close to or to the end of it's adjustment range where has more difficulty at that point perhaps?? I am trying to figure out the overall deal here. Many times is not even recommended to clean the T/B bore as will become as before quickly, and the system is supposed to be designed to accommodate.

I would guess the IAC is not going bad needing replacement? Just not familiar with this particular instance.

Does require a theft-resistant torx to remove those IAC screws. Is not a regular torx. Got them somewhere but boxed up since i moved here to Utah. Bummer.

Thanks guys.

 

[Kejtar]

What CHarles said

 

[Ghost]

I had that happen to a ford too.....

93 Ranger. it was the TPS on that one. Is it possiable that your TPS is acting up?