I've got a 2001 (3246cc, 325bhp) M roadster. When changing gear or
approaching a junction when the clutch is depressed the engine rpm
sometimes drops below 500 then returns back up to the normal idle
speed. Also when accelerating it can very occasionaly have a flat spot
not too dissimilar to a misfire. I have taken it to my local BMW
specialist who has had it on the GT1 diagnostic system four times. Each
time it registered no fault on any electronic component. They did
suggest it could be the throttle position sensor, air flow mass meter
or a throttle return valve as these were servicable items on earlier M
powered cars. They also told me that an electronic component fault
would have to stay on for about 10s for it to register in the ECU
memory so even though it comes back OK on their machine it could be
Has anyone else had a similar fault or has any other ideas to what it
For what it's worth, I recently experienced some strange throttle
related issues on my 328is. We replaced the throttle position sensor
and it hasn't reoccurred since.
The TPS has two potentiometers in it. One increases in resistance as
throttle is increased and the other decreases. The difference is
monitored. If one fails the discrepancy will produce a code, but the
faulty part in my car did not produce any codes.
One other possibility is a sticking idle control valve, which affects
engine operation below about 20% throttle. In fact, if it fails
entirely, the engine will die when you let off the pedal. I had to
replace that too, once.
Check my site for details.
Doug Vetter, ATP/CFI
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