hey scotty I am pretty stumped on this problem with my 86 Chevrolet 305 with a edelbrock 1406 carburetor. I have it timed to a perfect 4 degrees btc on cylinder one at 500 rpm on drive idle with carb and timing. The truck runs rough when in drive and foot on brake. I can drive it down road and once its up to speed it seems to work just fine but when its idling it sounds like misfire but I am not sure if its the spark plugs or if its something to do with the hei distributor and don't want to buy the most expensive part and it still do it. But I can take the number 1 cylinder spark plug wire off and it bogs down even more, but when I take number 3 off and then 5 after I put 3 back on it doesn't make a difference on bogging or anything the spark plugs were replaced 1 year ago about 6000 miles ago I normally only drive it about 20 miles a day for 5 days a week. but when I go to shut it off it trys dieseling and I have to keep turning key till it shuts off. it has no egr valve it is pretty much just the motor itself with ignition switch and basic stuff. would help if you could try to pin point it more then just several things. it has new spark plug wires and new fuel filter and carb is tuned and timing is good.
lassic signs of a worn out engine, like blowing head gasket. Also check for worn out carburetor since it diesels