Hi, I'm a newbie. I have received a great amount of info from here, but now I've got a problem I can't solve. Yesterday I removed the throttle body for cleaning. There was a lot of crud, gunk and stuff in there that I got out with a small brass wire brush and some brake clean spray. It was nice and clean when I reinstalled it. I hooked everything up and good seal around the intake elbow, checked and rechecked the electrics. Now my idle is about 1200 rpm when warm and will not go down. Makes for bad driving around town. Anyone have any ideas???


car is: 1995 XJS, 4.0L, 67,800 mi.

 

I'm going to make the most obvious suggestion first.

Are you sure you reconnected everything properly? There are those tricky coolant hoses on the underside, as well as the potentiometer. I would recommend unplugging, and replugging that potentiometer in.

Did you make sure not to spray any solvents in the throttle body that could have harmed the potentiometer? Damaging that would cause a high idle.

Did you do anything that could have caused the throttle body to not close all the way? At closed position, I believe there is supposed to be a .002" gap. A larger gap could cause a high idle.

Finally, you may want to reset the idle air actuator. If you check my posts, I believe I gave a step by step procedure to get that done.

Good luck and post back with responses and results!

 

I know what the problem is: you used 'brake' cleaning spray instead of 'throttle body' cleaning spray.
Easy mistake but make sure that you don't use throttle body cleaning spray on your brakes.

 

Thanks folks for your replies. A little bit about myself. I've been wrenching for 50 yrs. I have successfully rebuilt Mercedes and bmw engines. Even the bmw m52 dual vanos engine. So I have a little experience. Back to the throttle body.
When I cleaned the throttle body, I removed the idle control valve and the throttle position sensor. I used the brake cleen on bare metal only. Everything was reassembled in proper order. The reason I cleaned the throttle body was the accelerator was sticking badly at idle. There was probably 1/8 in. of gunk on the manifold side of the throttle body. No more sticking accelerator, but have high idle. I'm going to disconnect the battery and let it sit overnite. I've only had the car for 3 weeks and I just love it's style and the drive. There were actually 2 things wrong when I got the car. The 2nd being that the climate control panel is dead, temp sw not working, fan will run on high at 1,2, or 3. All fuses are good. I really appreciate you helping me out. thanks

 

Sometimes it takes a little for the idle to come down. Sometimes you have to have it reset with the Jaguar PDU.

Could also be the idle control valve

 

vac leak would be my educated guess.

 

I thought I had my high idle fixed. I replaced the weak rubber throttle body intake boot with a high performance 90* chrome intake and couplings. Sensor and vent were threaded in nice and tight. Added a K&N performance cone air filter also. Neat system. Bought a good used idle control valve known to be good and installed it. Started it up and right off the bat 500-600 rpm idle!!!!. Super!! Shut it down and restarted, 1000 rpm. Next time 1200 rpm. Next time 800 rpm!! I have read that maybe I need to have the EMC reset. That is just plain stupid. Electrical circuits either work or they don't. They don't work maybe half-way. I fooled around with the idle valve 4 wire connector and idle went down to 600. So I cleaned and tightened the contacts in the connector. 600 rpm, then 1200, then 1000. I love the car but I can see why Jaguar went belly up. To take a very fine AJ16 engine and have the Lucas electronics do the engine management was a very bad business decision. They sure didn't go to the same schools as Bosch electrical engineers did. One hardly ever has problems with German car electrical systems. Nuff said!!!!

 

Also, there are no vacuum or intake leaks. Just really dumb wiring in a great car.

 

I had my ECU reset by a shop that had the PDU and never had another problem.

I tried adjusting the IAC but I couldn't get the setting to stick. Did you try resetting the IAC? Perhaps it will work better for you?

 

Thanks Vee, I guess I'll give it a week or so. Then if it is still the same, I'll have the ecu reset though I still don't understand why. On every other ECU I've had experience with( Corvettes, BMW's & Mercedes ) the computers usually respond immediately to proper sensory input with proper output to respective valves and switches. I've said enough.

 

I still can't tell if you've reset the IAC. I've posted the directions before. I would give it a shot before waiting the week.

Do you know of a shop that has a PDU?

 

If you removed the TPS, it increases the chances that you need to ECM recalibrated significantly. Though the idle constantly changing up and down is a bit odd.

 

Is the PDU the only device that can recalibrate the ECU?

 

The Jaguar IDS or WDS software will be able to do all the various adaptations and recalibrations.

Also there are third party systems available that can do some of the recalibrations.