Intermittent idle issue

[Harrytsg]

Suggestions required please...

Yesterday and today on separate occasions, the car started and ran fine, after about 5 miles on the first occasion and about 15 (motorway) miles today the idle started fluctuating between 300-1500 rpm, but not regular cycling, also associated is a slight hesitancy.
Yesterday I stopped and ign off/on cycling the stepper it cured itself for the day, today I tried that again only to get high idle until I reached my destination.

Both journeys home were without issue.

I have (today) run through with my Ecumate and apart from my stepper not cycling from 0 position to circa 129 on initial ign on (which the instructions say may happen) everything appears normal, no fault codes either.

I also ran the car and wiggled the wires to the stepper and AFM, but could not recreate the problem.

Any thoughts?

[blitzracing]

Leave the ECUmate plugged in when you drive the car. When the fault occurs check the car is in idle status, as opposed to road. Check the speed reading is zero as well. You can also try putting say 30 open stepper pulses to raise the idle, and see if it then drops to where it should be after a few seconds, as the ECU compensates. This will check for a sticky stepper.

[Harrytsg]

Thanks Mark, I have left the Ecumate in the car ready for just such an occasion and will try what you say.

Ar ethe steppers known to stick?

[JFReturns]

Generic idling problem suggestions: clean stepper motor, plenum butterfly valve, check leads, check plug shrouds, check vacuum advance pipes.

[Harrytsg]

JFReturns said:

Generic idling problem suggestions: clean stepper motor, plenum butterfly valve, check leads, check plug shrouds, check vacuum advance pipes.

I did clean and check all the above except the plenum butterfly, also the the distributor cap and rotor arm (both cleaned until new ones arrive, but only a year old).
Checked the vacuum advance function as well, which sucks (sorry, couldn't resist).

But the circumstances suggest something either sticking or a broken wire, given that its intermittent.

[QBee]

85% of journeys my idle is spot on at 800 rpm
Every now and then I get a run where the idle is 2000 rpm. No logic to when it happens, just bloody irritating when it does, especially in traffic in town.

[occasionaluse]

Every time i hear of this problem i recognise it as the one i had which got worse and worse. I did the usual stuff, air leaks, stepper etc etc. Ignition amp is what caused it. Cheap and easy to replace - personally i would start there.

[Harrytsg]

So, went out in the car on Sunday, also too and from work today and ...... all fine.
So its either the cleaning of the stepper motor (spindle out, cleaned and greased) making Mark spot on with his diagnosis, or, its the Ecumate being left connected menacingly threatening the car to do it again.
My money is on the stepper (famous last words) and I'm tempting fate by saying so.

Thanks for the responses, if it recurs I'll have to admit it here.