I have a '93 960 wagon with 168,000 miles that has had me longing for another 740. Around 120,000 miles it started to stumble occasionally. Just one buck and then it would resume running fine. Took it to the dealer and they said I needed OEM spark plugs, not the single electrode type I had installed. A few weeks and one ECM later, it was running just fine again. Around 150,000 or so miles the check engine light started coming on again. Codes 231, 511, 512 and running noticably rich. These are the things I have tried over the past few months: new plugs (multi-prong Bosch platinums), new fuel filter, throttle body cleaned, new flame trap, new O2 sensor, one leaking vacuum hose connector replaced. Still, I have been getting these codes and that occasional stumbling. The real trouble began the day I pulled the spark plugs to inspect them and test the compression while I was at it. After buttoning it back up, it barely idled like it wasn't hitting on all cylinders, stalled and hasn't fired since. I was careful not to mix up the wires. Anyone with the distributorless ignition knows it is pretty hard to cross them up as the leads are basically the optimum length for each coil. I have tested for spark on #1 cylinder and smelled gas in it while the plug was out for the spark test. One would assume the trouble results from the last thing done, but I am at a loss as to what to try next. No codes were picked up trying to fire the engine. Any ideas as to what has been causing it to run rich and now not start? The next thing I plan to test is for spark on all six coils.

Thanks.

 

Make sure the wires didn't back out of the plugs for the coils.
You may have a bad coil for the stuble at times.
Also you may have a faulty mass flow sensor.
You can unplug the mass flow and try to start it.It goes into limp home mode.