'78 928 - weird problem - need help
 

OK. I am almost done getting my friend's car running. Now I have this bizarre problem. It is intermittant but here is the problem. You start it and it catches but when you let go of the key it dies. It did it about 4 times in a row. Then I found out if I keep the key in the start position(with the starter still running) It runs normally and revs - but as soon as you let go of the key it dies. My first instinct is that the lock cylinder is defective. Is there anything else I am overlooking?

The ignition switch (electical part-out back of column-2 screws) is probably bad, no terribly uncommon nor terribly expensive. Another problem may be wear in 3 areas: back of the tumbler; front of the switch; shaft that drives the two. Usually just replacing the elec. switch takes away enough slop to make it function again - start there.