Hello all. I have a 1989 740 GL sedan B230F and LH2.4 with multiple symptoms and problems related to fuel mixture/ratio. I began this journey with a post a few weeks ago about idle problems, but I've since realized that there are bigger issues.

The problems and symptoms are:

-Very poor fuel economy: On a good day of hiway driving I might get 15 mpg. Typically I get 12 mpg or less. Car is automatic with overdrive.
-The car runs rich: plugs have carbon deposits and a friend following behind reports black smoke.
-Occasional rough or varied idle speed. Seems to improve for a while after disconnecting battery.
-Occasional brief hesitation when starting from stop.
-Very recently, will not start when cold due to severe flooding. (The car can only be started by removing and drying the plugs, and disconnecting the injectors until it begins to run.)

The system consistently sets codes 312, 221, 213, and 113. The codes are not set at idle, but are set within a few miles of driving.

113 and 221 are both fuel trim codes, 221 says too lean but I know this not to be true.
213 says throttle switch full load setting faulty, and this may be true. I do hear a click when just opening the throttle, but have not tested full load.
312 says a bad connection with the knock sensor..maybe a bad sensor as the connection at the sensor seems fine.

I can't keep driving the car in this condition...Cold starting is an issue, I can't afford the fuel and I am sure I'll ruin the new catalytic converter

What I have done:

- Cleaned throttle body
- Removed, cleaned and tested IAC. ok.
- Replaced air filter
- Replaced O2 sensor.
- Replaced seals on fuel injectors
- Replaced ECT
- Replaced flame trap.
- Had exhaust system serviced by muffler shop, and also replaced bad cat. conv. (Manifold flange was missing two nuts, and gasket was leaking.)
- Replaced distributor cap, rotor and plugs.
- Replaced fuel pressure regulator
- Sprayed starter fluid about the intake manifold gasket, without any change in idle.


So I feel like I am down to the AMM and/or the ECU. I realize as I am writing this that I have not checked the connections to the ECU. Any other suggestions? Have I missed something?