My 1995 Pontiac Bonneville cranks over and starts, so it has spark, full tank of gas, just won't keep running. I turn the key and it fires up then dies immediately. The only way the car keeps running is by keeping the key half turned between start and on. Any ideas?

Sounds like it might be a bad ignition switch. What does the security light do if you turn the key to the run position? See if it goes out after a few seconds.