Classic/Antique Car Repair: 1969 Lincoln Mark III Turning Ignition Off Problems, lincoln mark iii, dieseling

Question
Hi, Vern,

I have a 1969 Lincoln Mark III 460-Engine, 4-barrel.  After the car runs and heats up (at least 10 minutes of running), turning the ignition off in the park position causes dieseling and sputtering, and the car just keeps (roughly) running.  If I put the car into the drive position and turn off the ignition, only then will the car shut off.  I just got the car out of the shop (for a series of problems), telling them what the problem symptoms were.  But it seems that no one did a thing to address the problem; it's still happening as if it never went into a shop.  

I need an expert opinion before I go back to the shop to complain about the problem not being addressed.  Thanks much for your insight and assistance.

Answer
Hi Mario:
You are experiencing what is known as "Run-On". This only happens for one or two reasons...

1. Either the car is still idling too high after warm up. If this is the case, your automatic choke is stuff. Remember, after about 3 to 4 minutes of warm up, you have to tap the accelerator to release the automatic choke. This will idle the car down to proper idle speed. If this is how you are warming her up, then your problem is most likely #2. Otherwise try this procedure.

2. Cars have a "Run-On" solenoid that cut the air intake supply went the ignition is turned off. This solenoid is most likely bad. Also, if the car is not idling down after warm up, your choke could be sticking or the idle is set too high.