[JW89225]

Hi, have a knocking sound thats intermittent only on idle. Goes away as soon as any rev/gas is given,

Knocking sound does not go up with rpm, oil level is good. Coil/plugs/injectors changed last year.

[E90N52Xenon]

is it a knocking sound or more like a tick? On my N52 my vanos bolt failed and caused a tick (which is sometimes covered under an extend warranty)

[JW89225]

just a knock, not tick. Doesn't correlate with engine rpm, infact, give it a little throttle or during cruising at zero throttle and any rpm above idle the noise is gone... idler pulley?

[jadams161]

Take the belt off and run it. The air conditioner compressor pulley bearing fails and it sounds like and engine knock.

[bmw325i]

Originally Posted by jadams161

Take the belt off and run it. The air conditioner compressor pulley bearing fails and it sounds like and engine knock.

Good idea. Mine was making a noise at a gas station after a long drive. I turned it off to look at it and when I turned it back on the ac pulley sheared off. I took the belt out and drove to a motel across the street with no power steering.