Hello to all and first time posting!

I need some advice as to what's causing the problem on my carand i think i may be there(ish)
For about a year now I have been trying to narrow down the cause of a high idle. When starting up, the idle will go up to about 1400rpm. If i then drive off, I am more than likely to get the trans warning light come on after about a mile or so and when slowing down to enter a junction or similar. Vehicle will either go into lumpy gear change mode or restricted into say 2nd gear. No way of telling which until it happens. I will then turn the engine off the on again,and this warning will never reappear,no matter how long the journey.
Also the engine will appear to suffer from momentary loss of power,as if no fuel is getting to it for a split second.However,once the engine is up to normal operating temp,it will behave perfectly.
However, if I wait for a few minutes from first starting the car until the revs have settled at about 1000-1200 then neither of the above will happen.

I hope you are not too bored yet as this is where i think i have gotten somewhere at last.
If I start the car with the outside air temp at 25c or about that, the car appears to idle correctly and will fall to 750rpm quite normally and never suffer the aforementioned problems whatsoever. It will drive all day long and for 100's of miles and still be running correctly at journeys end.
But when air temp is colder,especially in the winter months,it really never settles properly most of the time.
I have also noticed the cooling fan appears to be running all the time and i am sure this was never the case before.

It has been looked at briefly by Jag but they said sticking accelerator cable. I need to point them in the correct direction before they start changing unrelated parts!

If Air temp seems to play a part in this, can someone advise what the cause may be?

The End. Sorry for a long post but otherwise the car is immac. and this is bugging me somewhat.
Thanks

Mark.

I've done battle with high idle as well....although it was never a temperature sensitive thing in my case.  Most recently the cure was adjusting the throttle cables. Weak return springs can play a part in the high idle bugaboo as well.

You're description of the symptoms has me wondering if perhaps you have a couple different problems. Just speculation on my part, mind you.

Cheers
DD

Thank you all thus far for your comments. I think i will take to Guy Salmon at Crawley unless anyone knows of a indy in East Sussex who knows their stuff. Will let you know the outcome.
PS what sort of cost involved in getting the tensioners replaced as mine starting to become noisy?
Cheers
Mark

Don't rule out something simple like dirt on the throttle cable, the mechnism where it attaches to the throttle body or the cruise control slider.
Cheers

I am not familir with XJR engine mangement but from your original post it seems to be temperature related.
Your car will have a coolant temp sensor
I think it will have an IATS (Intake air temperature sensor)
Your air flow meter will be hot wire ie temperature sensitive.
There may be an additional IATS sensor between supercharger and manifold.
All these sensors rely on resistance / voltage so if input voltage is wrong they can give wrong outputs.
You battery will give lower voltage in cold weather or just after starting, Second start with hot engine will not have such voltage drop. Voltage drop occurs for a while after start as battery recovers from starting current. Low battery volts could also be causing transmission fault indications.
My advice would be to check all connections to above components, your ECU earth and monitor battery voltage with an accurate meter.
If that fails find a good specialist with engine management diagnostics.
Cheers

I think I have the opposite. My engine (AJ16). runs smoothly and fine and is totally responsive, most of the time. Over the last couple of days it has stalled when drawing up to stop. I’m thinking crankshaft position sensor but any other ideas most definitely welcomed.

Nick

Just to update after a lengthy trial and error period. The fault appears to have been a dying TPS which 4 weeks ago left me with a car that would not idle below 1100rpm.
I was getting the gears holding for too long before changing, and an overfuelling that was causing the car to momentarily have no power whatsoever. Took the car to XJ Restorations in Eastbourne under its own steam(it never did actually breakdown) and after having the diagnostics done by a professional who could read and interpret what was the problem, a new TPS was fitted and that was calibrated to the ECU and IACV. Now I do not get even the tiny hesitation I used to get when setting off with a cold engine and accelerating to about 30mph. Impressed so far and to finally have the car running properly.

mallard63 wrote on 21.01.2012 at 12:58:22:




Glad to hear it's all sorted. The holding-gears-too-long thing is generally a clue that the TPS is suspect, or so I understand.

Cheers
DD

2jagsDoug wrote on 27.04.2012 at 13:44:09:


The tc throttle valve actuator is not a complicated thing but if you disassemble it I would recommend that you mark the position of the position feedback pot on top so you can put it back in the same position, and the lower gear is spring loaded with a clock-type spring so make a note how much it unwinds when you lift off the quadrant gear (so you know how much to pre-load it when you reassemble). Also be careful when you lift the lower gear as that clock spring will want to escape! The motor is staked together (I think that's the term) rather than having screws so I did not try to dasassemble that, just sleeved the wires.
Rads