got a problem that I've been debugging for a few weeks now with a Motronic 3.2 (now a 3.4 with 964 cams) motor, several calls with Steve Wong who has provided some debug tips but so far cannot find the issue. It's a new build with a S.W chip that fires up fine but will stall and won't hold idle for a few minutes. As soon as it warms up just a bit it's fine from then on. Here's my debug so far:
- Idle switch closes and resistance check show's it's working fine
- Disconnect the O2 sensor - doesn't seem to have any affect one way or the other
- CHT sensor is brand new
- Fuel pump, fuel pressure regulator brand new, fuel pressure checked and in spec.
- Injectors fully reconditioned, don't suspect them as the car pulls fine once warmed up
- Pulled the Idle mixture screw (the 3mm hex bolt on the bottom of the AFM), cleaned the air passages with brake cleaner. Closed all the way and backed out three turns.
- Re-tracked the AFM wiper, check with a 9v battery shows a monotonic output voltage across the range.
- same DME with a stock chip passes CA smog in my 1985 no problem
I'm out of ideas. Still think it's the idle mixture but adjust the screw on the bottom of the AFM doesn't really seem to change the behavior. I don't have a wide-band AFM to double check the mixture though.
Any thoughts as to what else I might try aside from spending the $300 for an AFM? I'm out of ideas.
Thanks in advance.
Bill