My motor was running great. No problems until about a week ago it started stumbling and the "check engine" light would flash. I took it to get scanned and the said it was cylinder #3. I checked for spark (good). I replaced the plug and wire. I also replaced the fuel injector. The engine light does not flash anymore it just stays lit but the car doesnt run better. It's a 3100 with 137000 miles. What the heck?