540i M60 running problem-stumbling, etc

[JKBe30m3]

I have been battling with this car for a long time now. I finally installed a new(to me) wiring harness and got her back on the road.

Problem: Stumbling on acceleration, cutting out on power when cruising. It feels like it is surging. Power comes and goes and the idle varies.

Alusil motor, BTW

Quick rundown on recent repairs:

Replaced O2 sensors
sparkplugs
tested coils(resistance well within spec)
Tested Idle control motor
No vacuum leaks-reseal not to long ago
good alternator(replaced a year ago)


Any ideas?

My next step is to take it to an local indy service center.

They will proceed to tell me that I have $10000 worth of repairs to make which I probably do. But I do my own work at my own pace. It is a third vehicle and not a priority. ANY help whatsoever would be greatly appreciated.

[Tiger]

ICV Valve... might as well do intake manifold gasket too as you do have to remove this to do so.

MAF

Crankshaft Position Sensor... must buy dealer only... aftermarket parts are junk. This is the first thing I would change.

[JKBe30m3]

I have already replaced or checked the items you mentioned except for the crankshaft posistion sensor. I'll check that sensor today

[632 Regal]

intake gaskets are almost impossible to check for leaks as the ports run not only on the outside but the inside of the intake manifold, also the front and rear plate gaskets leak. While in there look into replacing the intake valley pan as those leak also. My ICV was sticky but wasnt the culprit.

[jofusfarr]

I used engine starter spray to check for intake leaks...you can get it under the plenum with some bending. Just listen for the idle change, it'll be quite obvious.

[JKBe30m3]

I have recently done an intake gasket and PCV gasket, so I don't believe that is my problem. Are the crankshaft position sensors something that go bad very often?

[Tiger]

Yes... on BMWs

[JKBe30m3]

Is there a code that should come up for that(as far as the check engine light)?

[Tiger]

Nope... just do a search on this forum on CPS... you will see all sorts of problems with no codes.

[jofusfarr]

Check fuel pressure if you can.

If anything to rule out any issues in that regard.