What are the signs of bad spark plug and spark plug wires?
carbon is formed in the spark area. improper ingnition also is an indication of a bad spark plug.
Lack of power or diminished power and a miss that occurs quickly are signs of a bad plug or wire/electrical problem. The best way to check for bad spark plug wires is very easy. If you are handy with a voltmeter you can check the amount of resistance in the wire. If you are not wait till night time open the hood start the engine and look for sparks around the wires. I had a problem like this that drove me crazy as it would only occur once in a while. Visual inspections showed me nothing. Started it up one night looked under the hood and seen #3 wire was arcing through the boot on the bottom side of the plug.