Ideling 1600 rpm onlywhen engine warm

Thread: 6.0 V12 XJS High RPM When Warm - Jaguar Forum.co.uk

www.jaguarforum.com/showthread.php?t=54266
Mar 3, 2013 - I recently bought a 1993 6.0 V12 XJS and when it is started from cold it runs ... to 1300 RPM so it wants to surge forward when braking which is strange. ...Classics · XJS 3.6,4.0,5.3 & 6.0; 6.0 V12 XJS High RPM When Warm ... You might want to adjust the aux (extra) air valve to bring the idle speed down.

High idle warm may indicate bad coolant temp sensor.

check out the idle control valve first

remove and clean or replace IAC (idle air control)

Sounds like you have a vacume leak on your brake booster ....with engine running have someone press the brake while you listen on the driver side by the master cylinder the large vacume line going to the booster behind the master cylinder is most likely the vacume leak...and if so you can get what you need at your local parts store ...

Check for vacuum hose leaks or component clogs. You can use vacuum pressure tester.
or turn the idle screw down.

Vacume leak or bad idle motor. With the car in park and running with the hood open listen for leaks moving your hand around the different hoses looking for a change in the sounds that you hear. The idel motor also makes the car idel up to 1500 RPM or so right at start-up then idel down, If it doesn;t the idel motor is likly. Check engine light is on when running? Test for codes, Follow code test charts don't skip any steps!.

the iac probably has carbon built up around it this controls the idle speed try cleaning it first,if not it could be a bad iac or a vaccum leak that the iac takes some time to compensate for to control idle.

possibly the coolant temperature sensor is faulty

check all your vacuum hoses and the throttle body itself for a vacuum leaks if the hoses replace as nessasary if to check for throttle body get can of carb cleaner and spray around base of throttle body and sides not in it if idle raises you have a vacuum leak goto a good parts store and ask for a rebuild kit don't goto auto zone or advance they don't carry them