I've had an on-going engine "issue" (multiple issue) with my '89 740 (B234F):

First I was getting a consistent check engine light and several symptoms: bad mileage (~10 MPG), exhaust smell (how on earth do you describe an odd smell??), rough idle, black exhaust on hard exceleration. O2 sensor was replaced, check engine light returned, along with symptoms.

Then I changed mechanics and went to the dealership. ECT was diagnosed as shot and was replaced along with thermostat. TPS and fuel pressure both checked out fine (or so I'm told, and have no reason to doubt ... never knew a dealership to NOT replace/repair something if it checked out bad). The mechanic at the dealership told me I needed both fuel and ignition ECMs, which I didn't do because he wanted $2000 (I posted a message about this, thanks to those who replied). Mileage has improved a bit (~12 MPG) and check engine light stays off now, but idle is rougher than ever (~600 RPM) and now I've even stalled once.

Checked the OBD today and get codes (which return immediately on restart after clearing):

2-3-2 Fuel trim (lambda control) too lean or too rich at idle

2-1-3 Throttle switch full load setting faulty or grounding short

3-1-2 Signal missing for knock-related fuel enrichment
Wiring break between EZK terminal 4 and FI #28

So I don't know what to do. I'm guessing the 2-1-3 code could be due to the failing ECM, since the TPS has checked out fine? I've read through the FAQs, but I'm not sure of the best route: clean the throttle body maybe? I'd sure appreciate any thoughts.