Classic/Antique Car Repair: Chevy 454 dieseling problem, chevy 454, stop screw

Question
We recently purchased an old motor home ('86) and am very happy with operations, except for a continuing dieseling problem.  We've gone the tune-up route but it didn't seem to help with this issue.  I've read about Seafoam and it doesn't seem like a safe bet for us.  What can  you recommend?

Answer
I assume that you are talking about after run when you shut the engine down. The main cause is a throttle opening too much on shut down. I believe that there was an idle solenoid on that engine when new that when you shut the engine off closed the throttle. If the solenoid is there the idle speed is set with it and the closed throttle position is set with the idle stop screw. As far as I am concerned "mechanic in a can" products are a cover up. Just my opinion.
Brad