"Occasionally idle has going to about 2000 RPM on start up and slowly it will retard to normal. This sometimes occurs when slowing down and bringing it back into idle. Motor has 330 hours on it. I changed the plugs to Iridiums with the same basic NGK numbers, gapped to .040, and still have the problem now with an occasional loading up or misfire of maybe 1 plug. Old plugs were burning normal with no fouling or overheating. Plug wires were on tight. Do the new plugs cause the computer to "learn" this new scenerio? Thanks"