Idle Problem

[shed]

Hi all.

In the past week I've started to encounter a rather strange and un-nerving problem which I assume to be gearbox related.

The car is fine from cold, engaging gears in good time, and generally behaving as I'd expect, although I do on occasion suffer from a jerk on upshift from 1st to 2nd which I've read about in another post.

Once the car has been driven for some distance, and everything's had a chance to warm through things change. The box still changes ok, but when at a standstill the engine behaves as if it's likely to stall.

By moving the car out of D and into neutral the revs pick up a little and even out, however, leaving the car standing, running, for a couple of minutes can result in the same problem occurring.

Once under way again, all is as smooth and responsive as you'd expect. Any ideas what the (no doubt expensive) problem is likely to be?

Thanks in advance for your help on this one...
Ed.

[kelsham]

Hi You dont say which car you have? If a V twelve it sounds like an idle problem, most times I have found this to be caused by the auxilary air valve. Does the car tick over at approx 750 revs min? engaging drive puts a load on the engine.

[shed]

It's a 4.0 ltr (AJ16)

[poprivet]

Hello Ed, Could be a poor electrical connection. The TCU 'talks' to the ECU to vary engine idle speed with load. Its likely OK when cold as the mapping will be in a richer mode.
The box sounds like its doing all the right things which is good, although if the fluid and filter are of some age it would be prudent to change these in any case. I believe the TCU memory can be interrogated which may help if the problem continues.
Pop