Oh yea I'd bet it is!!! (archive)

Scottie, That is NOT a vacuum solenoid. First of all the wastegate does not operate on vacuum. When the knock sensor see that the boost exceeds 10 psi the unit sens a signal to the solenoid valve to open. The hose on the bottom of the solenoid is connected to the boost side (pressure side) of the turbo. When the valve opens this allows boost pressure to travel out both hoses on the top of the solenoid. One hose goes to the wastegate the other goes to the suction side of the intake. This is so that full boost pressure does not rupture the diaphram in the wastegate.

What you must look for is vacuum leaks. I myself on my 745 had the same problem.(745 is my 3rd bimmer and newest) With help from Jens (who needs to put what he knows into book form) I did two things. First I replaced all vacuum hoses. When you do this you must use the best hose that you can find! The vaccum protion of the system must have NO LEAKS. Also you must check the vacuum relief/check valve in the firewall and the one on the HVAC.(if you are not sure of what or were it is I can Email you some pics)Next be sure that the vacuum side for the HVAC system has no leaks. Second several of us out here have modified our waste gaes to produce more boost. If you go past the 10 psi point you must do quite a few modifications to system. New chip (to over come the 10 psi boost limit) remap injecters and more fuel flow.

I am sure once you redo the vacuum hoses you will see the problem go away. These are great cars and with the knowledge of this board we can have fun for years to come. Hey it's quite nice to have a wolf in sheeps clothing.

Jon Jacobs
86 745i
86 735i
87 325i

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