My octavia 1.6i 1999 has recently started to idle high. Seems to idle either around the 2000rpm or 4000rpm depending on the mood it's in. Used to only happen with a warm engine but is now becoming more frequent. Any ideas, looking around people seem to be suggesting the MAF, but this looks pretty clean to me. I'll give it a clean anyway but if it's not this where could I look next?

I've taken a few items off to carryy out some simple fault finding, so have probably introduced faults into the ECU, is there any way of clearing this to reset the ECU.

Any help would be great, as it's getting anoying and I don't really trust the local mechanics for this one.

Faults logged by the ECU can be cleared with VAG-COM. If you post where you live there might be a member nearby able to help with that.

I have just had a look at what Autodata CD2 has to say about erratic idling and the 1.6 engine. There are so many possible causes that it might be best to let a dealer investigate.

Got the fault codes off the car today (following it idling at around 2000rpm and dying on me at a roundabout), see below:-

00522 - Engine Coolant Temperature Sensor -G62

00533 - Idle Air Control Regulation

00537 - Oxygen Sensor Control

Idling air control regulation seems to ring true as idle is all over the place, but this doesn't help answer why. Does this indicate a dodgy indicator or something else? Any thoughts?

The engine coolant temp sensor, now had a look at temperatures using vagcom and it was telling me that one of the sensors was controlling temperature well from 95 to 85Deg. (There was another reading labelled temperature on vagcom that drifted up slowly to around 20Deg, but not sure what this refers to, any thoughts?). Can't imagine the coolant temp sensor making the engine idle so strangely but I think I'll change it anyway. Is this the temperature sensor that sits in the return hose next to the engine or is there more than one?

Also had a look at the runtime data with it idling at around 1500rpm. Mass air per rev is around 141mg/rev. I thought I'd try with the MAF disconnected and around the same speed it seemed to be around 80mg/rev!!!???? The default schedule is half what the engine thinks it is. Now I'm confused. Could this be causing the oxygen sensor control fault or is it vice versa. Not sure if this is flagged because the sensor is duff or because the ECU is expecting a different level of oxygen.

Thoughts on the above would be great...

I had a less severe version of this problem when the adjustment circlip at the engine end of the throttle cable of my Felicia 1.6 went missing. I replaced the circlip but didn't put it back in exactly the same position as before. The car was downright dangerous to drive in traffic due to the often high idling speed. The problem was quickly cured by my dealer who recalibrated the throttle body using a 1551/2. (Sorry I didn't mention this in my PM to you).