M54 Pulsing around 3-4,000 rpms at mid throttle (video)

[GasBuggy]

Hi, first post. I bought a garage kept Z4 from a co-worker two weeks ago and have immediately run into this issue. This is my first BMW. It's a charming little car with only 51,000 miles.

I removed the DISA Valve and it appears to be in excellent shape and holds vacuum.

At light throttle and full throttle there are no issues. It makes great power and idles smooth. It will not start doing this until the engine is fully warmed up. I have premium fuel in it.

I am holding steady throttle until the last second when I go wide open.



I've been working on cars since I was little and have a garage with a lift. I don't plan to make friends with a new mechanic. I don't like throwing parts at problems but I did order a new OEM lower intake boot (upper is new) and a set of spark plugs.

 

[Pondy]

VANOS? The timing changes at around 3,000rpm on the M54. Could be that the VANOS is getting confused at part throttle?

 

[MikeyH]

Hello, welcome to the forum, hope you get your problem sorted soon.

 

[GasBuggy]

VANOS? The timing changes at around 3,000rpm on the M54. Could be that the VANOS is getting confused at part throttle?

I'm concerned that might be it. Because to me it feels similar to Honda VTEC kicking on and off. And perhaps the way it was driven previously the vanos wasn't engaging often?

Vanos is controlled with oil pressure and it seems that this issue is prevalent only when the engine has been driven 10 miles or so, by that point the oil is much thinner.

 

[GasBuggy]

I replaced the lower boot to the throttle body last night. I also pulled the coils and original spark plugs out (they were tight but looked ok)

Two coils have a significant amount of rust dust while the other 4 were clean.