Random idle speed

[matttav]

I have just put my 93 4ltr through its MOT after being laid up for a while.. IT PASSED! *Chuffed*

However, when starting it up she revs highly (over 2k revs) sometimes and even carries on climbing the revs after that.

On the road it takes ages for the revs to drop down after I have taken my foot off the go faster button, and occasionally the revs drop down enough to stall.

I have cleaned the stepper motor etc

Any pointers before I start to fiddle would be most appreciated!

Cheers
Matt

[parrot of doom]

Check the stepper motor chamber isn't worn at the end where it meets the valve, and sucking air through.

[tahiti450]

Other than the above; have you got an air leak elsewhere, anywhere on th industion side , check the hose from the stepper isnt cracked or any others.

[matttav]

Urmmm... just felt inside where the stepper goes in.. and feels ok. But tricky to tell.

Also noticed there is slack on the acc cable.. maybe this is stopping it return ok.. but seems inconsistant with the prob.

Ok I will check the hoses. If an air leak would that not create a problem which always reved very high?


Can stepper motors fail suddenly?

Cheers
Matt

[puffsorted2]

Make sure you get an air tight seal when u put back the stepper - don't overtighten cause u will break it, instead wrap a small piece if PTFE around the thread.

[raw-sewedge]

An other place to check for air leaks is the servo hose. They are cooked by the exhaust and crack allowing air to be sucked into the plenum that the ECU does not know about.

If your pulling more air in to the engine from elsewhere it will tend to raise at idle. Would be like holding the throttle slightly open.

>> Edited by raw-sewedge on Monday 12th September 16:59

[chimalsu]

my chim revs high when cold ie 2k but is as good as gold once warm

[glynlucas]

This can often be caused by a faulty coolent temperature sensor used by the ECU and is a cheap and easy part to replace. Other causes are a faulty Lambda sensor or other sensor used by the ECU to maintain a closed loop control on the engine.

[matttav]

Urmm.. the idle is totally random.. and can't find an air leak, and have PFTE taped the stepper in etc

Is there any way to test the Lambda sensor?

Matt