M60 cut-out problem

[Priit Varik <Priit.Varik@xxxxxxx>]

Hello,

My E34 530i with a M60B30 engine has developed a annoying intermittent engine
cut-out problem. The weird thing is, it does this only when engine has warmed
up. When starting out with a cold engine, it runs fine for the first 30-
40
minutes. Then the idle tends to drop low when idling and it may completely
stall while driving.
At idle the tach needle goes down to 500rpm and all lights dim somewhat.
The
cut-out appears and dissapears sharp - just as some electrical fault.
The other weird symptoms at this cut-out are: 1) The tach needle does not
drop
a bit 2) fuel consumption gauge drops to zero.
I have inspected the plastic parts of intake manifold for vacuum leaks and
cleaned the ICV all to no avail.
Various mailing lists suggest that the problem may lie within the Motronic
unit or with the bad rpm sensor.
Before trying to replace the expensive ECU, i'd like to test the cheaper
sensors first.
I've found some reference resistance values for both the cam and rpm sensors,
but I'm sure this static test won't reveal all possible problems. So I intend
to check their dynamic response with an oscilloscope.
What I do not know is what should I look for on these oscillograms?
What should the picture look like for a good-condition rpm and cam sensor?
What level should the signal be for ECU to correctly read it?
Are the two sensors interchangeable, i.e. can I swap them for test purpose
(someone mentioned in one archive doing so)?

And one more question has recently emerged in my head. As the car is equipped
with ASC+T, could a fault in that system have such effects? Is ASC able
to cut
and restore engine power instantly?

Any insight is very much appreciated.

Priit

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