I have a 1990 740 Turbo Wagon with the following reoccuring codes. 213 Throttle switch signal wide open (replaced switch didn't help). 312 Knock/ fuel enrichment signal missing. 231 Lambda adjust (probably because of the wide open throttle signal). I've checked the connections at the sensors and as far as I can trace them. The general condition of the car is excellent. Does anyone have any ideas? Maybe if the 213 and 312 connect somewhere together. Computer problem?? Thanks GV

 

You would need to check continuity in the wiring from the TPS and knock sensor all the way to the ECU. Does it exhibit any drivability problems?

 

How does the engine harness look?

 

The wire harness looks to be in good condition. The car is running very rich, probably because of the wide open signal, but is driveable. It idles rough. I can trace the wires from the knock sensor and TPS to about the drivers side wheel well where it goes into the main harness. Don't know how to trace it from there. Thanks for the help. GV

 

With those symptoms ,the harness should be tested at the ECU. But, I would also be suspicious of a bad ECU. If you can locate one cheap at the local auto recyclers ,or by prowling eBay, it may be advantageous to try a swap.