dead miss
 

got a dead miss in my 300 straight six. but only at an idle

You might start by looking for a vacuum leak.

You might start by looking for a vacuum leak. Look for any cracked vacuum hoses or possibly one came off.

if no vacuum leak then check and clean your spark plugs may have one fouled out i would bet that you still have a miss even high rpm's you just can't hear or feel it while you're giving it gas

If it will help any, Feel at the tailpipe with the engine at a higher RPM, if it is still missing you will feel the popping from the exhaust.

Easy way to verify a vacuum leak is to remove the intake hose/air cleaner and slowly start to choke off the intake air flow with your hand(s). If the miss goes away and the engine idle smooths out, you have a definate vacuum leak.

I think if there is no machine flow then examine and fresh your ignite connects may have one fouled out i would bet that you still have a skip even great rpm's you just can't listen to or experience it while you're changing it to gas . . . .