E46 3 series 1.9 idling problems (2002)

My E46 is suffering from a strange problem.
The revs drop down to 500rpm and the engine almost stalls before shooting back up to a normal 800rpm idle.
This happens usually when the clutch is dipped and accelerator released when the car is cold and/or heated rear window / aircon is on.
Anyone experienced similar problems or have an idea on a solution ?
Had the car in at the dealer and under extended warranty they have replaced:
-reversing sensor cone -full heated rear windw -heater fan -offside rear light cluster -wiring leading to each rear light cluster
I cant complain about getting an X3, Mini Cooper S or 320d from the dealer for a day every week but its not solving the core problem...
Lastly, car is a 2002, fsh, only 45k
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I had something similar with mine - e46 2002 similar mileage.
When stopped - at traffic lights etc. - the rev counter used to jump up and down a little - and the car used shake (like the engine was going to stall)
I brought to mechanic - he did a quick diagnostics test - all clear - then quickly said that the throttle body needed cleaning. He did that - and all fine since!
Hope this helps! Keith.

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Hi the fault with the car is probably due to the engine getting unmeasured air from somewhere, and the air mass meter cant compensate for it. it seems like the fault only occurs when load { a/c, demister }is placed on the engine.Also check the engine temperature reading in the DME control unit. You may have a faulty sensor there.
Clive B

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