e46 328i intermittent loss of power and rough idle when warm

[Gabriel]

I have a 12/2000 manual BMW e46 328i that has a strange problem. When the engine is cold, meaning not reached its operating temperature, the car runs perfectly fine, RPMs at idle stay where they should 650-700, and the might of the inline-six is all there.At operating temperatures, though, sometimes there is a noticeable loss of power and the car idles rough, RPMs are bouncing form 500 to 950, at which point the engine is at the brink of stalling, but doesn’t. If I rev it hard, while in neutral, sometimes the problem goes away, sometimes not. Switching the car off and on again, makes no difference. As long as the engine is at its operating temperature the problem has a 50-50 chance of occurring, which is mind-boggling as there is no obvious reason why. Like I said, sometimes I rev it hard and the problem disappears completely until the next day… other times this makes no difference at all. Sometimes it can drive for a weak with no issues, and then after that the problem appears every day for a month…

There are no engine codes that are stored, the car does not overheat, it doesn’t burn oil, at all and there is no murky goo on the inside of the engine oil cap. The coolant is also crystal clear, with no oil floating around inside the overfill tank. Disconnecting the MAF, makes no difference.

I have read through all of the BMW specific forums and while many have experienced this issue, no one seems to have resolved it.

Suggestions are appreciated.

Topic

[Richard Kirshy]

You state that unplugging the MAF has no effect on the engine.
It should…
My suggestion is that you should test the MAF for proper operation at operating temp.
Being that you say the Vehicle runs well while cold (open loop) I’m thinking the ECM is operating based off some predetermined MAF valve on open loop.
But when closed loop is reached that valve is not switching over to the actual MAF readings.

[Author]

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