Was: Rough .....and Dave CTed B." Having no more options I decided to check spark plugs once more. This time I decided to check-compare size and strength of sparks, not like before the condition of spark plugs...
My car was doing this recently. It was a worn rotor cap. Don't know how your engine gets its "spark", but if you have a rotor and cap, you might want to change them. It is a relatively easy job to do yourself. The few cars I've done it on required a screwdriver and about 20 minutes of time to change a rotor and cap. (change them both) Basically, the spark travels into a rotor, the rotor spins as the engine is running. As the electrically charged rotor spins, it contacts little metal points on the rotor cap. Each point on the rotor cap corresponds to a particular spark plug wire. At the other end of the spark plug wire is (you see it coming . . . ) a spark plug. So obviously, if there is a problem in the rotor-cap area, one or more cylinders is likely to not fire.
I'm guessing a rotor and cap will cost you about $50 at a parts store, but that's a wild guess, as it's been a while since I've done this, and I have NO IDEA what kind of car you drive. If your car HAS these parts, they should be changed periodically anyway, probably every 50-70K miles or so. They don't last forever. Hardest thing about the job is keeping track of where all the plug wires go when you disconnect them to replace the cap. So you might want to make yourself a diagram or something before you remove the wires. For that matter, you might want to replace the plug wires also, while you are at it. Won't cost that much more to do so, and you'll be doing most of the labor involved if you replace the rotor cap. Besides, the symptom you describe could ALSO be caused by a bad plug wire, so you'd be eliminating one more possible problem.
But if your car's engine doesn't have a similar spark distribution system, ignore all of the above. -Dave
