Hello All

Got an interesting conundrum for you all.

The situation is that I've got a dodgy idle on the AX.

What happens, is that the idle can increase up to 3500 rpm sometimes, and will just sit there, then it *might* go down. This happens randomly, eg: I could be sitting at the lights and it would happen.

This problem also persists when the engine is switched off over night. Sometimes though, the car is fine.

Now, a little bit of background on the AX idle system. It has an idle motor, which is a 12v DC motor (a Johnson 540) attached to a worm drive, that goes into the throttle body. It has 4 pins on it. Two of the pins go to a microswitch, which is closed when the throttle butterfly is close, and open when the butterfly is open. The other two pins go to the motor.

The car controls the idle by either sending +12V or -12V to the motor, opening and closing the butterfly.

Now, Ken W and I have tried a different idle motor unit, and that didnt fix it.


The other interesting symptom is that there seems to be a short between the two wires that go to the throttle butterfly switch. This short only exists when the ignition is on, so it seems like an ECU problem, rather than a short in the loom.

Does this sound like a reasonable assumption?

Any ideas of other things to try?

Cheers Ken.

(NB, in the mean time, i have disconnected the idle motor cable, and permanently shorted the two throttle butterfly pins closed. This is because when the fault doesnt exist, the ECU has problems calibrating the throttle potentiometer, as it seems to think that the throttle is always open.)