Irratic Idle

[Mentor]

My car sometimes when stationary will not drop the idle down to 800rpm. Sometimes it will fluctuate between 1000 and 1200 rpm. Any reasons why it could be behaving this way? By the way, this is after the initial start up high idle. Thanks.

[b14]

faulty temperature sender?

[Mentor]

I don't think that would cause a fault like this, though I could be wrong. any other suggestions or ideas people?

[andybnwc]

dirty throttle body? had that problem on my golf quick clean and it was fine again

[Bluebrakes]

When does the symptoms start?

Cold?
Hot?
Both?

Don't rule out a temperature sensor, whether it is air intake temp sensor, etc.

ideally you need to read the fault codes using vag-com.

[Mentor]

The symptoms start a majority of the time when the car is hot.

[Mentor]

If it is an air intake temp sender, where is this located on the car, is it an expensive part and is it easy to fit?

[Mentor]

Would a faulty air intake temp sender affect power aswell?

[dazzer]

Would a faulty air intake temp sender affect power aswell?

I expect so - I think the ecu carries out a speed density measurement. The density of air is affected by temperature, as well as other things such as altitude. The fuelling is delivered accordingly so the fuelling could be out. I think that's a fair description.

A faulty coolant temp sensor could be causing you fuelling issues. A common problem experienced with the sensor is failed starting. The ECU operates in open loop mode I believe until the engine is warm enough. Open loop means that the ECU will enrich the fuelling for cold start up. If the sensor is buggered then it won't deliver enough fuel for cold start up - fuel doesn't vapourise very well in cold air so needs AFR needs to be very rich to get the engine started.

[Mentor]

Coolant temp sensor seems to be working fine. I had a faulty one before and the water temp gauge was all over the place, sometimes reading 90 then 60 then 0. I'd have to agree with you that the fueling does seem to be off, but because of what remains the mystery.

[Bluebrakes]

Ideally i wouldn't keep guessing what sensor has gone.

Get it on vag-com and cut to the chase.

Look on vag parts .com to check for a rough price. They do tend to be slightly dearer.

[Virdee Autos]

AFAIK the air intake sensor is part of the MAF.

As has been mentioned, best to get it diagnosed instead of guessing.

[dazzer]

AFAIK the air intake sensor is part of the MAF.

As has been mentioned, best to get it diagnosed instead of guessing.

AIT sensor is in the inlet manifold IIRC.

[Bluebrakes]

AFAIK the air intake sensor is part of the MAF.

As has been mentioned, best to get it diagnosed instead of guessing.

I would be very worried if it was done inside the maf.

For a start the MAF is a hot wire type, so it would be measuring its own heat.

Secondly the air goes through the turbos, intercoolers, etc so the temp will raise and fall as it goes through the system.

I prefer audis location. On the throttle body boot (G42 sensor i think).

I'm only have a gentle dig at you. More of a reason as to why its not done by the maf.

[dazzer]

Getting confused about the sensors under discussion now.

AIT sensor in Intake manifold.
MAP Sensor in TBB
MAF sensor after Air box and before turbos