Hello,

Ok here goes..I have an extremely high idle in my 1996 jaguar vanden plas xj6. let me tell you what I have done..all hoses have been replaced and are perhaps a week old. I have had a compression check done on the engine a few yrs ago and it was in great shape. I had the transmission solenoids checked. The ecm was reflashed a week ago. I have replaced the cam sensor,crankshaft sensor, throttle body, throttle body position sensor. Idle air control valve, air mass flow meter. They are 3 yrs old at best. The car has 110k miles on it. The car recently went from a high rpm of 1500 to 2100. It goes up to that every time with no change and stays at 2100. Thats where it stays when it idles. I replaced the lucas idle air valve with a generic one (made in china) and bought 3 chinese idle air valves.The cam sensor had been moved in the past when the ecm relays were shot and no one could figure out why so the cam sensor had been moved around. I had my mechanic pull apart one of the chinese valves and compare it to lucas..it was the exact same threading and length of valve as he was worried that perhaps the valve to regulate the air flow was too short or the threading was off on the inside. Nothing. He has checked for vac leaks 3 times and nothing. Is there a setting on the cam sensor? is there some way to check the idle and adjust it MANUALLY? We are both at our wits end..if I replace the motor or the ecm will the problem go away? Any ideas?? Thanks

*Update*..I had jaguar attempt a throttle adaptation reset with NO success. ECM showed no issues either.. Crankshaft Position Sensor has been replaced as well and still the idle is high. When the car drives after 44 miles per hr it jerks as if the Idle Air Sensor is confused and cant figure out to cut the air or add more mixture. I am having a very difficult time and any help is GREATLY appreciated..thank you...

 

Welcome aboard :-)

High idle problems are common. Many here are well versed in the adpation/re-learning procedures and can perhaps pass along some helpful info. They'll chime in.

I myself have battle high idle problems and was lucky enough to discover that the throttle cables simply needed re-adjusting. That's something you might wanna consider....as well as stronger return springs.

Good luck
DD


PS- I hate to harp on your very first visit but postings written as a overly-long, single paragraph are hard to slog through. Hint hint :-)

 

I hate to suggest this but it happened to me right after I cleaned my throttle body on my 95 XJ6. I know this sounds dumb but I had high idle also. Went to my indy and he looked at it and asked where the electrical connection was on the throttle body. I showed him and in so doing I showed my self that I had forgotten to connect the computer cable to the throttle body.

I told you it would sound dumb.

 

Sometimes the plug brakes on the idle position senser under the throttle body.Easy to do when taking the oil filter off thats what happened to mine anywhy.

 

I had the same problem when I first got my car. Doug is right start with the cables as their are two of them I backed both of them off.


I then adjust the one attached to the throttle body till it gave me 700 to 750 rpm's. Once I had that done I adjusted the cable attached to the throttle pedal just so the RPM's came up just a tad. Then I locked it all down. Over the next few days I did some slight adjustment till it felt right for me.



Hope this help some I’m sure others will have some other things to pass on to you to help as well.


Good luck

 

From what you have written i will assume that you are confident there are no air leaks in the intake system. I will also assume that the ISCV works correctly and that the ECM correctly recogbnises the closed throttle beecause the throttle adaption has been performed. I will aslo assuem that the throttle butterfly does not stick because you have replaced it. Like Doug, I would suspect the cables themselves. Will it idle correctly if you disconnect the cable from the quadrant.

If none of this works, you might want to blank off the vacuum signal that goes to the Rochester roll-over valve that prevents purge vapour leaving the fuel tank when the engine is not running. I have read that these valves can fail causing an air leak into the inlet manifold. I can't picture where this vacuum signal hose joins the intake system, as I have an XJR. What i can tell you is that the steel pipe and then vaccum hose follow a similar route intothe engine bay as the fuel lines. This should help you trace this hose to the connection point on the inlet manifold.

 

This might be the place to ask about the throttle position sensor TPS. If one disconnects the throttle position sensor at the bottom of the throttle body and then readjusts the idle using the idle screw on the side of the TB along with cable adjustments will the computer operate OK without the TPS input? Will the economy be effected?

I think my TPS has a bad spot at idle which causes stalling at idle sometimes. And one solution might be to operate without it in manual mode.

 

Hi,

Thanks to you all for your insights into the TPS adjustment.
I recently cleaned the Throttle Body on my 1997 XJ6 4.0 as it was not running as smooth as it should.
After re-assembly the engine was revving at around 1500rpm while idling. Everything appeared to be connected OK, but it seems I needed to play with the TPS to get it to sit in the correct position.

After a few tries reseating and repositioning the TPS the engine is now revving at 750rpm and is running a lot better than before.

Thanks for your advice, it really helped give me confidence to try again before going out and buying parts.

 

Same thing happened to me right after I cleaned the throttle body. Idled around 1500. Turned out that I had forgotten to plug in the connection on the bottom of the of the throttle body. Got lots of help but no one told me to plug the darn thing in. Very embarrassing and got lots of comments.