Idling away ( I wish)

[Tafford]

My '94 4.0l chim was getting an increasingly erratic tickover so about three weeks ago following advice on another thread I disconnected (just pulled the plug out) the stepper motor. This gave a marked improvement - much nicer to drive at low revs, reasonably steady tickover. However, the revs still seemed to fluctuate at tickover by 100rpm or so. Last night and again this morning it suddenly refused to tickover at all, just dying completely nearly every time I stopped. It will occasionally tickover at about 500rpm. What other than the stepper motor could cause the revs to fluctuate at tickover? What could cause it to stop ticking over at all with the stepper disconnected when it's been happy like that for three weeks (gets used nearly every day)? BTW - water temp doen't seem to make any difference at least not last night / this morning - it's the same cold or hot.

[Ricardo Bertone]

Reconnect your stepper motor and then if you haven't already reset your ECU - switch ignition off, disconnect plug on top of ECU, wait a few minutes and then reconnect.

Ricardo

[andy-w]

definately something else causing the irratic idle...i have had me stepper disconnected for a while now and it has remained solid....takes a little while to tick over in the mornings....maybe 1 minute but after that it doesnt move.

Possible ignition problem?

[else]

I did the same as you but found the revs dropped steadily until it wouldn't tick over anymore, over about 3 hrs driving time. I turned the engine off and reconnected the stepper motor which restored the tickover to how it was before.

I reckon the stepper motor moves on its own due to vibration, maybe some more technically minded PHer could explain how that could happen.

Try blanking off the pipe that goes from from below the butterfly at the inlet to the plenum to the stepper motor itself. flattening it with a clip of some sort will do this and then adjust the tickover using the adjustment screw near the plenum inlet.

Andy

[GreenV8S]

It sounds as if the stepper motor is moving on its own. I've driven with the stepper motor disconnected for a few hours and not encountered this problem, but it seems that you're not the only one to encounter it long term. At least the initial experience shows that the engine idles steadily with it disconnected which means you can rule out any other major problems affecting the idle. It's normal for it to hunt slightly, but if it's excessive this could be a sign that it's running rich, or has a lumpy cam, or an AFM incorrectly calibrated/becoming inaccurate, or the wrong vac capsule [for the cam], or any of a dozen other possible problems. If it's only hunting slightly I wouldn't worry about it though unless there are other symptoms to suggest a problem. Now you need to decide whether you are going to try to get the stepper motor working correctly, or disable it in some way. For example, blocking off the air bleed hose that feeds it would disable it. You would need to establish the right idle speed using the base idle adjuster, best avoid using the throttle stop if possible since this will also affect the overrun cut-off.

[Tafford]

OK thanks all - looks like first thing to try is to reconnect the stepper, get an steady idle, block off the vacuum pipe, disconnect the stepper again and see what happens. If that cures it at least I know it is the stepper moving on it's own. I much prefer driving it woth the stepper diconnected - apart from the first minute it's much smoother and has a steadier tickover.

Edited by Tafford on Thursday 23 November 16:14

[kenny chim 4]

andy-w said:

Possible ignition problem?

I'd tend to agree and suggest HT leads starting to break down. They degenerate quickly due to underbonnet heat.

Worth checking in any case..