[bbowden]

2009 335d, full deletes BRR tune for a couple years. Have been chasing a bizarre issue for a couple months. No boost on initial start below 2100 RPM. Let it warm up shut the car off and back on again, power is restored. All new vacuum line, pressure converters and vacuum control valve. 27 inhg at idle, maintains while driving unless something is being actuated.

I think the culprit is the turbine switchover pressure converter, have replaced it twice. On initial start outlet will be right under 5 inhg, after the restart will jump up to 27 inhg. Have manually supplied vacuum to the turbine switchover can on initial start, low end power was restored. Also tested both pressure converters through ista and they passed.


Thought maybe it was MAF issues, logged it in testo and it seems to align with other logs I've seen. Any ideas what would cause this?

[lnxguy]

Are you getting 27 inhg from the vac pump to the input of the PC that controls the turbine switchover on start up? That's what I'd be looking at. Vac pumps are known to wear out, definitely an item you'll want to replace at higher mileage.

[maryjane]

Long shot but look to see if the changeover rod is catching/dragging on the heat shield. If its bent at all it can hit it.

[bbowden]

Ended up replacing the MAF as a last resort. Resolved the issue, power is restored. I believe the air mass part of the sensor was reading correctly based on testo logs, makes me wonder if the intake temp was off or if it contributes to turbine switchover. Either way if someone else has this issue check the MAF.

[nonford]

Love it when the resolution is posted!! Good job!!!!