Please do not assume that the following is the culprit for SidMiller's issues, as the previous threads contain valid root causes, but I do want to add that the VANOS unit could be a culprit, as similar symptoms are experienced in other BMW engines with known bad VANOS units. The nature of VANOS failures do not necessarily generate Fault Codes, which is why this unit is such an illusive failure.

The E36, E39 and E46 have a high level of failure in the VANOS units due to the seals that are used in the units, which do not hold up well to synthetic oil and high temperatures. Why would BMW use correct seals in the X5 engines?

Before someone jumps on me for possible "bad" information or hi-jacking this thread, I am looking at the VANOS as the possible reason for my 2005 X5, 4.4i which is experiencing the following (similar to SidMiller's issues):

1. Bad MPG (<16 MPG highway - easy throttle)
2. Rough Idle (notable at cold start, but present at other times)
3. Poor acceleration under 3000 RPM (always)
4. Valve chatter (sometimes - sounds like clicking)
5. Engine noise from VANOS area (both sides of engine - sounds like a muffled chainsaw)

This all started around 14000 miles, after the dealer changed oil and left it 3 quarts low, which required me to return to the dealer after engine started #4 stated above. They took the car around to the service bay and they returned it shortly stating that nothing was wrong, but the oil "magically" was full.

Unfortunately, the seals that fix the E46 vanos units offered by http://www.beisansystems.com
probably won't fit the V8 VANOS units (N62 bi-VANOS). I want to get similar seals and rebuild the VANOS units on my vehicle and I will provide my findings to this forum.

(ref: BMW X5 Service Manual, p 100-7, Bentley Publishers)