Erratic

[Germs]

Why is it the tickover on my 450 serp Chim can be rocksteady at 800rpm one minute and 2 mins later can race away at 1500rpm and 5 mins later just about struggle to tickover? The car has had a major service a month or so ago (this problem predates this and foolishly I didn't mention it when I checked it in) and the stepper motor was cleaned by me about the same time. Apart from that it runs very well.

Bloody annoying!

As always, thanks for any help.

[Flintstone]

Damn!!

I misread the thread title

[Germs]

We could come to an arrangement if you can give me the answer!

(Do I need to shave my legs?)

[GreenV8S]

Those symptoms point fair and square at a problem with the stepper motor.

Dirt on the stepper motor or housing seems to be the most common cause of problems like this. It's conceivable that you have an intermittent wiring fault, faulty stepper, faulty connection in the ECU etc. Hopefully just dirty though.

If you want to prove this, then get the engine up to temperature and idling steadily then plug the stepper motor. If the idle speed immediately stops mucking about then you know it's the stepper motor causing it (rather than some underlying problem). Incidentally it's fine to drive around for a few hours (or even days) with the stepper disconnected. If you're considering running like this longer term you will find that the stepper motor gradually adjusts itself and you'll need to find a way to disable or immobilise it.

[sapper]

Ive had exactly the same problem. I reset my stepper motor last week and had 400 miles since yesterday without missing a beat.
Do a search for resetting stepper motor. if you cant find it ill did it out and type it up.