Hello again, yes me with the problems

I am still having a problem with the idle speed of my XJS HE V12. Started from cold I get a high idle that gradually comes down to about 900 rpm (in neutral), however, if I turn the car off and restart it, the idle is a consistent 700. If the car is started warm then idle speed is 700 and all is fine. But if started cold then it's 900 and will never go to the normal range until restarted. This leads me to question if the thermotime switch is working? It does seem that if water temp is low then it does what it should but as the water temp increases it doesn't seem to shut off of its own accord - is my thinking right or flawed here?

ANy ideas how to check it?

P.S. when it is idling properly at 700 rpm then the idle seems 'washy' like the mixture is too lean. I wonder if the mixture has been set to take into account the enrichment the thermotime fault (?) is delivering?

 

Are you sure you have a Thermotime switch?

The Thermotime switch, cold start injectors, and cold start relay were part of the cold start system that Jaguar abandoned circa 1983-84. I'm pretty sure a 1985 car wouldn't have any of it. In any case, the system operated only when the starter motor was engaged so, unless there was a very weird fault, it wouldn't account for a running problem after the engine was started.

Perhaps you're thinking of the CTS- Coolant Temp Sensor? It controls enrichment for cold running. Often gives problems but, in and of itself, shouldn't change idle speed

The AAV-Auxlliary Air Valve control engine idle speed while the engine is warming up. Often gives problems.

There was a recent thread that outlined a similar problem where turning the engine off and then restarting gave some sort of idle RPM result. I can't remember the exact details or if a final conclusion was drawn. Some were wondering of one of the timers for the vacuum advance system was malfunctioning.

Cheers
DD

 

Not sure of anything with this car! What it should have, it doesn't and what it shouldn't... The problem you describe at the bottom of your post is exactly what my car is doing and resolves once the engine has warmed a bit and is then restarted. Not really a major problem but jolly annoying 'cos I HATE faults, especially ones I don't understand.

Any chance you can recall the other thread?

Also, I have just changed the coolant injection sensor and the temp gauge sensor along with thermostats and rad caps.

 

https://www.jaguarforums.com/forum/x...rs-v12-208870/

Cheers
DD

 

Thank you very much

 

It is still doing it though I have checked everything I can find. Also, it is now doing it (could have been always doing it) if the car is left for a few minutes and then started: 900 - 1000 rpm but goes back to 750 if the engine is stopped and restarted. Also the air intake on the passengers side is MUCH stroner than on the drivers side (RHD UK car) is this just the AAV doing its job?