My 1990 760 turbo sedan will only start when cold, then runs for 2 to 3 minutes, then dies. When I ground the cold start injector and open the throttle (a little) it will then start and run at about 2k rpm (without cold start grounded), but it will not rev above 2k. then if I open the throttle it will stumble and then as throttle is opened more will (lean ?) backfire. If I then ground the cold start injector while it's running, it will rev up, and at over 3k will run and rev normally, (at which point I can disconnect the cold start injector ground) as long as I keep it over 3k. I have replaced air mass sensor, O2 sensor, pcv and air mass to turbo hoses (also plugs,wires cap, rotor, and air filter) and injector /ezk temp sender, and checked fuel pressure. Both fuel injector and Ezk ecu show 111 codes (I've replaced both units). I Have checked for vacuum leaks, all sensors, connectors, wires and fuel pump relay/fuses, all seem to be correct. At level 3 check at diagnostic terminal, fuel injectors,idle valve and cold start injector all work. It worked fine till one morning when the car wouldn't start. Orginally failure was probably air leak in air mass to turbo hose, which i subsequently replaced. Could this be a knock (enrichment) sensor problem. Any ideas or suggestions?