My 2004 330ci has had lack of power/acceleration in the higher rev range (3000-4000 rpm) along with error codes P0171 and P0174. After reading many posts online it appeared I had a bad DISA valve. I tested the DISA and observed it did not close at engine start up, so I thought I had a bad DISA valve. So after replacing the DISA valve I thought all was good, but I still have the same issue. The new DISA stays open and does not close at start up, just like the existing DISA I replaced. I checked all the wiring and connector to the DISA valve, all appears in good condition. The car idles just fine, no issues, it runs ok during my daily commutes, but when accelerating in any gear (4th gear is most noticeable) once I get to around 3000 rpm the power diminishes. My next step is taking it to BMW for a full diagnostic thinking that it might be a software issue. Any other advice or recommendations are much appreciated. Alan
Additional information: When I turn the ignition key to position #2, there is power supplied to the DISA valve and it is making a humming noise, but the valve does not move/close as it is supposed to, it only makes a clicking noise when power is applied. I have done same with engine idling with same results. Also performed a bench test with same results, it only makes a clicking noise, it does not activate the valve. It seems that there is something else needed to activate the valve. With the symptoms I described earlier it could be that the valve is working in reverse, with the valve remaining open at idle and closing when getting in the higher rev range of 3000 - 4000 rpm. This could explain the lack of power/acceleration I experience at the higher rev range, when the valve is supposed to open.
I found this video explaining the vacuum needed for the disa valve to operate and how to test it, hope this is helpful to other members with similar disa valve issues. I know now that I have a vacuum leak somewhere and will need to find it and fix it. https://www.youtube.com/watch?v=pg6Jb3qEYvM
