My xj x300 revs at 1500 and and drops to 1200 on tick over its auto replaced air controll valve is ther a some thing else that i need to do over than that car runs rich but fine

 

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I've moved your post to the X300 section.

 

Welcome also.

I am having trouble really getting to what has been done. One looooooong sentence for us OLD folk is not the easiest to decipher, and I gave up mind reading when the teenage kids grew up.

I am assuming that your location is in the USA?????.

If so, your market has an EGR (exhaust gas recirculating) system, and it reeks havoc with idle, as I have read on here in the archives.

A grubby internal bore of the throttle body also causes all sorts of idle nonsense.

 

I am in england and the car has no egr and the throttle boady has been changed the car runs fine but the idel is 1200 should be 600/700 engine has done 147000

 

I had the same problem and did all the usual things, cleaned throttle body, checked and cleaned idle control valve (they can gum up and get a bit sticky internally). I also had the throttle position sensor reset by a Jag main dealer, but the problem persisted. I finally sorted it, months ago with no re-occurence, by adjusting the throttle stop screw. This is a very small grub screw, with an allen key head, located down on the left hand side of the throttle body, when looking at the throttle body from the passenger side of the engine bay.

It can be accessed with an allen key (though you may need to shorten it slightly) and turned back, to allow the throttle to close more fully.

Before doing this though, check for any build up of crud on the actual "stop" tab that comes to rest against the end of this grub screw. You will see the tab and can reach it easily. Give it a wipe clean, as any build up will affect idle.

The throttle return spring can weaken over time also and can be tightened by rotating it an extra turn on the spindle, giving it more tension. Better still to replace the spring with a stiffer upgrade. This was a procedure which Jaguar adopted due to common high idle problems.

Good luck with it!

 

Thanks for info i have just had a look at what u said but problems still there thanks enyway

 

start with the basics. I would first adjust the throttle cable and see if when you give it slack the idle goes down, if so, your return springs are bad or the cable is getting hung up somewhere. the accelerator cable return spring and the throttle return spring on the throttle body, they can be worn and not returning the throttle plate to a good seal. you can also check the position of the potentiometer at idle with a scan tool, check to see if it is within acceptable limits. dont forget about air leaks, they can rise rpms.

 

thanks i bought a second jag cheep because of rust and that engine ran ok on idle so i took all thing conserning my problem of that car and fitted it to mine still ran high in idle