It's a high mileage '91 325iX, and suddenly today, at cold, it cranks,
fires and starts fine but the engine won't stay lit unless I
continually goose the throttle. It's not engine speed related, I can
goose it up to 2,000 rpm but when I try to hold it there, it dies,
like it's not getting fuel.
Bentley says that a vacuum leak has to be huge for Motronic 1.1 not to
be able to adapt to it. All the vacuum hoses appear to be connected
and intact, so I'm guessing that's not it.
Bentley says test the fuel pump next. Maybe, but the engine will run
smoothly so long as I keep goosing the throttle. Doesn't *seem*
the fuel pump's bad, does it? Maybe it's not seeing the engine speed
signal and I'm somehow compensating for that with the throttle
Bentley says that Motronic 1.1 cold starting is entirely managed by
the ECU, so there's nothing mechanical to check in the cold start
system. It seems like something isn't seeing and/or reacting to an
engine idle signal or condition, though.
No fault codes are present.
Any suggestions for what to check next? I'm an M20 newbie, so be
gentle with me.