Cold running problem

[raisbeck]

I've been wrestling with a problem with my daughter's 318is for a little over a year. Basically, the car starts on the first crank and idles just fine, but when the revs hit 1500, it cuts out. I can't tell whether its cutting off the fuel or the spark, but it dies, precipitously. As soon as the tach drops below 1500, it runs fine. If you hold the pedal to the metal, it shudders and shakes as the tach oscillates between 1400 and 1600. The whole phenomenon is tied to the engine temperature. As the engine temperature increases, so does the cutout speed. By the time you've driven a couple of miles, you can rev it to 6000 with no hesitation. Once the engine has run for a few minutes, it won't do it again until tommorrow.

The obvious explanation is something to do with the coolant temp sensor. I replaced it, checked it with an ohm meter at various temperatures, and it seems to be within spec. The car was intended to be a family project, so at various points during the last couple of years, all of the vacuum hoses have been replaced. The cam and crank sensors, and associated wiring have been replaced or checked out. The air flow meter and temperature sensor check out ok. The throttle position sensor checks out with an ohm
neter. I cleaned the idle control valve and it seemed to help a little bit, but didn't eliminate the problem. I replaced the fuel pump relay and pressure regulator, and the fuel pump is within spec for pressure and flow. I replaced the plugs, wires and the single coil that didn't check out with an ohm meter on general principles right after I bought it.

The code reader says that there's a problem with the cam sensor despite the fact that its new. It checks out with a meter, and so does the wiring between the sensor and ECU. If I wait 'til the car is warm (i.e. the water temp gauge is off the peg) and reset the ECU with the code reader, it won't throw any new errors until tomorrow. Last week the code reader said that the oxygen sensor was bad and shut up after I replaced it.

I've seen a number of similar stories on the net, including a couple on this BBs, but no one has posted an answer to the problem. Probably didn't have time once they figured it out, or maybe they just junked the cars. The only thing that I can think of that I haven't tried is the ECU. I don't have any idea how to go about getting a reliable unit (there are several used units available on ebay, but ...), short of spending big bucks for a new factory part.


Short of spending a bunch more money, does anyone have any ideas?

[Blackice]

I think there are 2 temp sensors on the M 42, have you checked both ?

DAve

[raisbeck]

Originally Posted by Blackice I think there are 2 temp sensors on the M 42, have you checked both ? DAve

Yep.

The sensor at the forward end of the block talks to the computer, the one at the firewall end is the gauge. I replaced the former, but both met spec with an ohm meter and boiling water, and, if the aft sensor doesn't work, the gauge shouldn't.

Its getting down to the ECU, but I still haven't figured out how to get one I can honestly trust.