1996 XJSC 4 liter fast idle

Could it be the stepper motor ? Thanks , Jeff

Could it be the stepper motor ? Thanks , Jeff

Had a few minutes to play with the car this evening. I was going to pull the throtle body again and get the part number for the TPS. I found the rubber tucked in ,fixed and replaced all. Started fine but idle was still high. I played with the throttle and all at once it dropped to 900. Thought all was good and let run and reved fine. Cut the car off and would not restart for several tries , then fast idle again. No codes. I may have got TB spray in the TPS when cleaning. Any ideas ? Thanks , Jeff

Had a few minutes to play with the car this evening. I was going to pull the throtle body again and get the part number for the TPS. I found the rubber tucked in ,fixed and replaced all. Started fine but idle was still high. I played with the throttle and all at once it dropped to 900. Thought all was good and let run and reved fine. Cut the car off and would not restart for several tries , then fast idle again. No codes. I may have got TB spray in the TPS when cleaning. Any ideas ? Thanks , Jeff

Jeff, you need to have that throttle adaption run with the diagnostic equipment from Jaguar.

I did remember that there are two other pieces of equipment that will usually run that adaption. In addition to the Jaguar PDU, a WDS and a GenRad GDS500 or GDS510 scantool will accomplish the task. Most dealers should have access to one or the other. The most reliable device though is the PDU.

What you describe will take a long time and a lot of driving to correct itself.

Hello all and thank you for the replys. The car was idling fast to start with. I had the same thing happen several years ago and a good cleaning fixed it. Drove the car tonight for the first time since the cleaning. Idles out of gear at 1350. Drove it for 20 minutes and returned home. Pulling in the yard it started a mild acceleration of several hundred RPM's. Any help appreciated. Thanks , Jeff

Edited on 2010-08-25 15:56:40

The engine management systems on all '95-'97 4.0L XJ6's and all '95-'96 4.0L XJS's are the same.

There is NOTHING WRONG with cleaning the throttle bodies as long as the proper care is taken. If the throttle potentiometer is not removed, the bore should only be cleaned with a rag dampened with cleaner, not sprayed and soaked down with solvent. That can damage the potentiometer. Also, the potentiometer screws unfortunately have Loc-Tite on them. Gentle heat from a small butane torch is usually required to get them out without breaking.

Normally aspirated cars have a vertical throttle shaft, while supercharged cars have a horizontal shaft with the throttle body mounted under the intake manifold.

About the only reason we have had to replace a throttle body is when a shaft or shaft bushing wears and causes the throttle to bind and not return to the closed position properly. When this happens the throttle can be closed by hand to bring the engine speed to normal, proving the engine management is not the cause of the high idle. I did find a shop here locally that will machine a new shaft bushing and press it in, making the throttle body like new.

I can't imagine why your dealer would not clean your throttle bore, I'm a dealer and do it any time a car is presented with a sticking throttle. It makes any AJ16 engine a pleasure to drive again.

I would be cautious driving a car with an improper [too high] idle speed, waiting for it to hopefully adapt itself. That's not very safe, and rough on brakes.

From the answers I have gotten to questions, the TB is oriented differently?
Is your normally-aspirated unit horizontal shaft?
I was told the one in question is a vertical shaft, with TPS on the bottom.

Not sure if the engine management system is the same as my '95 XJR but whenever I clean the throttle body it takes a day or two of city driving for the idle to relearn and normalize...during which time it is higher than normal.

(Oddly, I've cleaned the t/body on a normally aspirated 96 XJ6 4.0l and had no such problem...proper idle right from the get go).

I'd give it a day or two and see what happens.

Several years ago there was a long, long discussion on JagLovers about XJS 4.0 high idle problems and the difficulties in solving them. You might wanna do an archive search there.

On the X300 sedans cleaning the t/body almost always fixes the problem.

Cheers
DD

Throttle bodies on these cars do not like being cleaned.
Cleaning fluid goes straight down the shaft and kills the TPS.
You may need a new throttle body.

If you removed the throttle body and TPS, then you may be okay.
Otherwise you need a throttle body.

Local Jag dealers will NOT clean those.
And, from what I've ben told, those throttle bodies have issues anyway.
What they are, not sude, but I did hear the word "seals".

Dave

Edited on 2010-08-24 22:20:05

Once you have tampered with the throttle body and the base air gap, the throttle adaption has to be reset. By cleaning the throttle, more base air is passed to the engine causing the higher idle. Resetting requires the Jaguar Diagnostic device called a "PDU". Trouble is, it may be hard to find a dealer that still has a functioning PDU.
Right now I don't know of any other device that can reset the throttle adaption.

Good luck!