Idle While still in Auto V8 ?

[R1CBM]

Evening all.

Hope all is well.

Just wondered if anyone had any ideas as to why (only sometimes) when the engine is hot in my 3.9 V8 auto disco, I stop with Auto in drive, foot on the break. Sometimes the idle drops and rises. Nearly stalled on my a couple of times.

I've checked the connections to the coil and they seem find ?

[Budgie]

Does it do the same if you shift into neutral or park? If not then it may be nothing to do with the engine.
Have you checked the fluid level in the auto box? It could also need a gearbox oil change or the gearbox oil cooler may not be doing its job.

[R1CBM]

If I shift to N then the engine picks up a bit as normal. Idle is fine.
Only 'sometimes' when under D and I am stationary. I think there must be something controling the idle that's not quite right, ?,,,,,, scratch head :dunno1:

[Budgie]

I think I would still be looking at the fluid level and the filter in the sump of the auto box, when was the last time that the filter was checked?

[gadgetman]

If its only doing when you have got your foot on the brake, it might be worth checking the servo pipe for possible leaks,there is also a check valve in the servo, where the pipe goes in, check to make sure you can only blow one way through it,,

[R1CBM]

Thanks for the replys

I've checked the service history and the gearbox has had a full service within the last 20k miles. The fluid level is OK.

[R1CBM]

Update: Looks like this issue is not just while the engine is under load, but in N or P it's ide is not smooth when hot. Any ideas ?

[tomm]

Just noticed this post,, Mine was doing exactly the same until eventually it did start stalling on me.
Lived with it through sheer laziness and stuborness until next service which cured it funny enough !!
Mechanic said that it just needed the (plenum?) cleaning out.
Think it was the 'box' after the airflow meter. Could find out if you still have prob's.

As an aside,, problem was always exaggerated after filling up at local Tesco garage. Was noticeably better form other stations.

[R1CBM]

Thanks for that. I think you could be right, I had a friend that works for Ford power and he suggested something round here could be a loose wire hence intermitant

http://www.rimmerbros.co.uk/v8engine/images/ld28a.gif

[fnscotsman]

I had this problem with my 95 Discovery (3.9 v8). Turned out to be the Idle Air Control IAC valve (or Stepper motor as they call it in the USA). This basically controlls the idling speed. For some reason they seem to be notoriously bad for failing and causing all sorts of idling problems. I also have a 94 disco (3.9 V8) and I have had to replace the IAC valve on them both.
My stalling problems would happen usually on hot days. As you pulled up to traffic lights the revs would oscillate and finally the engine would cut out. I would re-start, the car would run like a champ for a while. (I usually had the Check Engine light come on also.)
You could simply remove the IAC valve, and check it for oil or gunk build up. Clean it if it is dirty and re-install it. If the problem persists you might want to replace it.

Good luck.

[R1CBM]

Have removed cleaned and replaced. Couldn't get a fibre washer so used some thread seal. Will test tonight :bigun2:

[t0ny99]

I'm with FNScots'...if the engines hot, perhaps the extra load of the cooling fans running is just enough to stall it. My RRC does it when hot too, and I've taken to left-foot braking...just not after driving the Audi, as the left foot thinks it's a clutch pedal. With amusing consequences!

Let me know how you get on, as I should probably do mine AND clean the plenum!

[R1CBM]

Didn't work, I'm going to order a new one.. :behead: