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XJS high idle HELP!!

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R

Raptor

Freshman Member
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Greetings,

I have a 1996 Jag XJS with 90,000 miles. For the past couple of years, the car has been plagued with poor gas mileage, occasional stalling and an occasional fury of 2,000~3,500 rpm high idle periods. Each trip to Jag costs about $1,000.00 USD and a different story about why there was a problem and why each time the problem was different.

Dirty throttle bodies, cracks in air inlet tube, defective idle stepper motors, cracked vac lines, rpm sensor, temp sensor, etc.

The latest visit to the shop was for the high idle. I explained that the stepper motor was replaced about six months ago and it made NO difference when it was replaced.
This time, after 7 days of diagnosis, they said that the stepper motor "fell apart" when they removed it. Upon closer inspection, they pulled the actuator rod out to "grease" it and it would not go back in. During this trip they also replaced the RPM sensor claiming that "although it did not read bad, they thought it was the problem."
Anyway, another $1000.00 USD and it worked fine for about 1 week. Now the idle it back up and worse than ever.

QUESTION: Are the stepper motors designed to be "pulled apart to be greased?" And, why is the idle speed such a problem?

Thank you!
 
I am assuming that your XJS is a six and not a twelve since the six uses the stepper motors. The stepper motor should not be taken apart as it is a Jaguar unit. The stepper could not cause such wide deviations in idle speed. Look for a major vacuum leak in the intake manifold. If it is a 12 cylinder then the vacuum leak applies double. Who are you taking this car to for servicing? Jack
 
Here is an update concerning the high idle.

I brought the car to a local shop that was recommended via the forum. This shop got me for another $1000 although part of that went towards new brakes (burned up because of high idle). This shop replaced the mass air flow sensor, added a ground wire and reset the "parameters." The idle held for 1 day.
Upon returning to the shop, they "searched" for days and determined that the problem was the fact that the 1996 uses a OBD I ignition system that, in 1996, was prone to failures as a result of the high battery drain. They installed a battery kill switch in the trunk and explained that I needed to turn off the kill every day or the computer would re-set to the high idle. When I questioned why the idle had not been a problem for years, they had no answer.
With no other options, I contacted the Jag factory help line via email. After going back and forth with them for months, I finally got a real person who stated he would research the issue. I am still waiting for a response.

Meanwhile, as summer heats up, I did notice that if the engine gets really hot, the idle suddenly works properly -- until it cools again. The difference is, when cold, the idle will start at 1300 and, as soon as you start moving over 1mph, the idle speed goes to 2500. IF you take it out of gear, the idle will hold at 2500 until the car comes to a stop where it returns to 1300. WHen HOT, the idle is 900 and returns to 900 in neutral while moving.

Obviously, there must be some problem with a cold enrichment feature. Any ideas?????
 
Just a hunch. If your car is V12, I think it has an AAV on the rear of the left side of the engine. This valve operates with a wax bulb similiar to an automotive thermostat. Go to jag-lovers.org and search the archives or download "the book" for more info.
 
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