My 1986 928S was running rich when I bought it, it was involved in a small fuel line fire. The PO, also the second owner, did a poor job of repairing the motor, now after doing a front end :TB, WP, Tensioner rebuild and numerous other things including the intake and cam cover gaskets, new hoses and vacuum lines. The car started fine idles fine but is running extemely rich. Any ideas where to start, maybe I won't have to go backwards. Thanks Jack

 

You could try testing the Output Voltage of the Ox sensor at the test port on top of the water bridge, to be sure it is working. I think the default no connection or bad is to run rich.
Also Temp sensors can be tested with ohm meter cold and hot for correct output (check each terminal lead to ground). There are writeup here for correct readings.

 

What makes you say it's rich?

Engine temp sensor or fuel pressure regulator.

 

Thanks DaveK9 was going to start that in a few days, might just replace the o2 and temp sensors.

GlenL, the exhaust in the garage is very strong, even ventalated, but no smoke. Thanks.

 

Either the O2 or the Mass Airflow sensor is faulty. Those are usually the two that cause rich condition but it could also be the fuel pressure regualtor. Make sure you test every part before deciding to change it. Throwing new parts at it can get really expensive very fast.

 

have you check to verify that all the diaphragms in the fuel dampers and pressure regulator are intact and not leaking? if you have a bad diaphragm it will run rich as the vac line from that unit will draw fuel through the diaphragm directly into the intake.