[dhspring]

Spark plugs are dirt cheap, one to 4 or 5 bucks each depending on what you buy, it could be a lot of things also, bad plug wires, how long since they were changed? If someone recently worked on it, they could have caused the problem as well. It could be the gap, it should be around 0.060" but check the tag on the radiator. Check all the plug wires to make sure they are properly attached to the plugs. Just do some minor checks before running to the shop and save yourself some jack. Also see if you can isolate a missing plug by pulling off each wire one at a time, while the engine is running, to see if you can find a missing cylinder, then check that plug and or wire as the culprit.