BMW Repair: E-38, manifold gaskets, mass sensor

Question
John, Was getting rough running with some fuel trim codes on my 97 740iL. The mechanic discovered an air leak at the diaphragm in the valley pan area and replaced it. Also replaced 1 fuel injector. They released the car to me yesterday running like crap. I barely made it home check engine light blinking all the way. I hooked my OBD/CAN meter up and now have a multi cylinder mis-fire code and two specific mis-fire codes on 3 and 4. The air mass sensor was cleaned but not replaced. They now want me to throw $400 at that. Is it likely, that's the problem?

Thanks

Answer
It's always tough to diagnosis anything over the web, and especially to contridict a mechanic who is seeing the car.

I know the air leak he fixed.  My guess is the intake manifold gaskets are either bad, or weren't seated properly when the intake manifold was removed. Or, if it's misfiring continually, the wires to the coils or the coils to the spark plugs aren't attached.

If you're capable of simple repair, I would check your wiring and coils on 3 and 4. If they are OK, I would look at removing the air intake and checking/replacing the intake manifold gaskets.  Not a tough job, just a time consuming one.