M20i dieseling, and slow start... occasionally

[Funkmasta]

alright, the (89)M20i in my 87 cabbie will occasionally diesel long after the key is out. WTF? additionally, after this happens, it takes a very long time of cranking for it to fire on the next startup (up to 10 seconds!)

-Still using the 87i harness and ECU.

89 motor has 220k on it, but is in quite good shape.

any ideas?
What would cause it to diesel?

[Hadrian]

Extremely hot exhaust valve?

[Funkmasta]

Extremely hot exhaust valve?

Maybe it is running lean?

Maybe not...
It passed emissions last week with flying colors.

I am at a loss here...

[Ablice]

Do you run it at low revs a lot? I did that with my 325e a lot. I'd rarely go above 2500rpm.

This is what you need to do for a start: On your way back to work, say, on the last 4miles of the trip, put it at 4000-5500 rpm, more like 5000RPM. Let it really cook in the combustion chamber for a little bit.

Come home, shut it off. Then clean out the fuel injectors. Come back in a week or two and tell us if it improved. The high revving on my 325e would hold back the dieseling and rough idle when cold for about a week. I knew the fuel injectors were quite due for a cleaning too.

[jlevie]

Carbon build up in the head and leaking injectors would be my guess. Since power to the DME should be removed when the key is out there shouldn't be any injector firing pulses, thus the injectors would have to be leaking for dieseling to occur.