QuestionI have a volkswagen jetta 2000 with 115k miles. No vehicle maintenance history. The check engine light comes on and felt a little vibration on the engine. OBD indicates P0303
( 3rd cylinder misfire). NEEDS ADVICE.
AnswerHey there Ruel; with only a single cylinder misfire it could be one of 3 possible components, and without the ability to test the engine myself, I can't tell you which of the 3 things it is .....most likely...
So, let's start with the least expensive, and the least difficult, and go from there.
First change the spark plugs...all 4 of them...because, I'll bet when you do, you will find something suspicious in the #3 hole, like water residue, or a coil on plug ignition coil that looks different from the others, and with no service history, it's just a good idea anyway. If nothing looks obvious, then the next thing to do is replace the coils themselves. We normally take the one from the cylinder with the misfire, and move it first to another hole, and then run the engine, and look to see if our misfire moved, if it did, then IT'S THE COIL. But, I'd change the plugs first, especially since you don't know when it was last done anyway. Make sure you've got fresh, good quality gasoline in the tank, and if the spark plugs don't fix it change coil positions, and check faults again. If it's still in #3, then you need to do a leak down test, and determine what kind of condition your valvetrain components are in. This should keep you busy for a while, but if you've still got misfire issues, get back to this forum,and let me know. I'll see if there isn't something else I can suggest then. Get busy, and good luck. Hope this helps.
