Just recently purchased 1980 L48 Corvette. My problem is that once the engine warms up it will continue running with the key in the off position (not dieseling actually running as if the key was still on). Sometimes it will shut down after 10-15 seconds. If I put the trans into reverse the engine immediately shuts down. Added info, previous owner installed an MSD Pro Billet distributor #8551, MSD 6A control module, Accel coil, Edelbrock Performer intake and 750 carb. I greatly appreciate any help in figuring this problem out.

Assuming it's an automatic, I would check the neutral safety switch because it seems like the voltage getting to the ignition system to keep it running has something to do with that switch.

1: Idle too high

Thanks for reply Adams Apple. Prior to addressing this issue I had to address the headlight doors not functioning properly. I have been through the vacuum system like crazy as I am sure a lot of C3 owners have. I was able to get them working correctly. It doesn't hurt to revisit this though you never know. As I responded to 73shark, I did pull up literature on the MSD system and found that there can be bleed by of current through it. I will more than likely convert back to HEI. The MSD system is overkill for this motor and it adds more equipment under the hood.

|UPDATED|9/1/2018 6:45:02 AM (AZT)|/UPDATED|

I agree that the first place to look would be the possibility of a fast idle allowing run-on with no ignition. Also the HEI system probably provides a hot or hotter spark than the MSD system does. I remember reading when they were developing the HEI system that they actually had to dial back the spark output voltage because they couldn't get good enough insulation on the wires to a stand it.