You are on the right track. The reason the idle has an impact on the dieseling is if the idle is set too high when the engine is shut off the throttle blades can't close all the way. Therefore if you have some hotspots and some residual fuel vapor from the carb it will keep running.
GM had a fix for this by having a solonoid that is energized with the key on to set the idle speed with. This way the idle speed adjustment on the carb itself can be set so the throttle is completely closed when the key is shut off and the solonoid de-energizes and lets the carb linkage fall back to the adjustment on the carb. It's a pretty slick setup and the same solonoid that's used to kick up idle speed when the a/c is on on some trucks.
I had one on the Qjet in my Nova and kept it when I put my Holley on it. Just needed a different bracket to hold the solonoid to the carb.
If all else fails, get used to shutting the engine off in gear and then shifting to park once the engine is off.
GM had a fix for this by having a solonoid that is energized with the key on to set the idle speed with. This way the idle speed adjustment on the carb itself can be set so the throttle is completely closed when the key is shut off and the solonoid de-energizes and lets the carb linkage fall back to the adjustment on the carb. It's a pretty slick setup and the same solonoid that's used to kick up idle speed when the a/c is on on some trucks.
I had one on the Qjet in my Nova and kept it when I put my Holley on it. Just needed a different bracket to hold the solonoid to the carb.
If all else fails, get used to shutting the engine off in gear and then shifting to park once the engine is off.
