Thread: Fast Idle problem-94 Disco V8

<span style="color:blue">is your stepper motor functioning correctly and not seizing up....?

that controls idle.....</span>

It sounds like you have an automatic ECU in the car, as this is normal behaviour with autos to smooth the change to first as the car comes to a stop. The ECU takes a signal from the Vehicle Speed sensor to tell it whether the car is moving or not. If moving idle up , stopped then normal idle.
The cold start behaviour sounds normal to me.

I remember several years ago i had a Falcon auto which did this and drove me mad in traffic. Went to the dealer several times ( who had no idea) until I finally read that it was normal.
regards Philip A

Thanks guys, but this is a 5 speed Manual 3.9 V8 injection. Not sure if the ECU is automatic or not..thats' too electronic for me..

And the stepper motor (ie IACV) is brand new from ULR in Malvern.

The idle is way too high as the idle prior to this wasn't too bad...

Basically, the engine maintains speed with the foot off the accelerator only until the vehicle comes to a complete stop..

I want to change components out, but would like other people's opinions before spending big $$ unneccsarily.

I've had similar (not identical) problems.
Mine would idle at 2500rpm until I had stopped for 20-30 seconds, when it would drop in steps down to normal idle. If I didn't get a long red light somewhere, it would continue until I had a chance to stop for a decent length of time.
I could be rolling along at only 5kmh, and it still wouldn't drop until I had stopped moving.
The general consensus here when I was chasing solutions seemed to be stepper motor problems.
Pulling the stepper motor off and cleaning it with carby cleaner has helped, but not completely solved the problem.
Since a new stepper motor is in the hundreds of dollars, I'm learning to live with it until it gets too bad to put up with.
Apparently, it's operation can be checked using Testbook at you friendly neighbourhood LR stealer.
I'd be interested to hear your solution when you find it. It may help me.

Good luck,
Ian

You have not mentioned the injection temp sensor. They only cost $30.
If it is rich and idling fast, it sounds like the ECU is cold compensating. Might only be a dirty connection. the resistance values are in the manual.

VSS should not be an issue. Does your speedo work?

TPS will not do this, usually anyway. Bad TPS most common symptom is miss while tipping in off overrun. In some circumstances, the car will cut out while just cruising along.
fuel temp sensor? This only compensates by a small percentage so should not cause the problem, but check the connections.

Bad IACV will usually cause stalling as you come to a stop as the car falls off high idle. the IACV on 3.9 is quite crude with I think only 4 steps. When they are dirty the usually just slow down in reaction, but should not cause avery high idle. What is the base idle?

Just thought of something. Could be a lot of crap around the throttle butterfly. Take of the rubber pipe and clean around the throttle blade, and take off the crankcase vent pipe and do the same.
This is my no 1 bet.
RegardsPhilip A

Ian,

thanks for the advice. My symptoms are very similar to yours, but I can live with it no longer. The fuel consumption has sufferred a little too long. As I said, my stepper is brand new and the old one was suffering a little.

Philip, thanks for your advice. Come to think of it, i think i will replace the flame trap and crankcase breather components. it's time to renew them and the flame trap was a bit crudded up anyway. Will clean the butterfly housing also as i haven't looked at that. The fuel injection temp sensor is what I meant and not the coolant sensor. The high rpm/rev problem is temperature sensitive, thats why i suspect an electrical/sensor component.
I have no cutout at speed and agree with you that TPS possible not problem. VSS-Speedo works fine although there is boucing in the needle up to 60 kmh, probably twist in speedo cable though.
Base idle is meant to be 525 +/-25rpm, mine is def higher than that. Will let you know how I go...Muddy

Philip,

Do you have the resistance values. I don't have a manual and only have Haynes to go by. Maybe need to invest in a manual!!
Muddy