Replace Your Spark Plugs

While you have your old plug in your hand, take a look at it. It should be a little dirty on the end, a little black with a little soot, the key phrase being "a little." If it's white or oily, this could indicate other problems so make a note of how they're looking. Also check to see if the porcelain insulator is cracked.

Finally, take a look at how the end you pulled the plug wire off is set up. Some will just be threaded like a screw, and others will have a large metal cap on the end. Be sure your new plugs are set up like the old ones were.