I have a 79 460 4v engine in a box van. It has been sitting for a lond time and had bad gas and was bending pushrods because of sticking intake valves. After removing the bad gas and loosening the valves and replacing the pushrods and replacing the spark plugs the engine seems to run pretty good. While the engine was running i noticed the idle seemed to be low so i removed the #6 spark plug wire to see if a noticeable drop in the rpm was present (checking to see if that cylinder was working because it was one of the ones that had bent several pushrods and the intake valve was really sticking). The rpm went up considerably. I plugged the plug wire back in and the rpm dropped. I did the same with all the other cylinders and only one other cylinder did that same thing (# 7). Could someone please tell me why?

 

Just a shot in the dark.... check the fireing order and plug wire placement/ routing. Then maybe the timing. Just a guess. OBCB