My 89 XJS V12 revs to 2000+ rpm when first started, after putting in gear and putting a load on it with brake it drops down to 700-750 and runs fine then. How can I slow the initial start down some, no need for it to sit there and roar for a minute or two.
Thanks,
DickC.

 

Sounds like the Air Idle Valve is failing. Happens to all of them at some point

 

I'll look that up, not sure where it is....should I have mentioned this is fuel injection?

 

AAV on the rear of the LH cylinder head.

Big alloy thing with Lucas cast into it.

Has a dumb 90deg hose on top the WILL split when you remove it.

I have rebuilt hundreds over the years, and have a Word doco on that procedure if you want it. Drop me a PM, as its too big to attach here, due to Kodaks included in it.

 

If Grant's suggestion doesn't fix it, you've likely got an air leak somewhere else. A close inspection of any hose that goes to the throttle bodies is in order.

Under the RH throttle body there is a large connection that, if not connected...or if the hose connected to it is leaking, can cause a big RPM jump.

Good luck with it,

John
1987 XJ-S V12
63,000 miles