I just got the jetta about a month ago. It has the 2.0 engine. Last week the CEL came on (sometimes flashes), The codes were a bad O2 sensor, bad temp sensor, and misfires on 1 and 3. I started with the Temp sensor, then did the O2, then I went ahead and replaced the sprk plugs, wires and coil pack. The misfires continue. I unhooked the MAF to see if it would go into limp mode but it changed nothing. Any suggestions on what I should do next.
Is it actually misfiring?
Check wiring harness at the injectors. Wiggle the harness and see if it creates a misfire, or triggers a code.
Check the harness connector (big round plug above trans iirc) for corrosion. Make sure pins are all clean and tight.
Check ground under battery tray. Lots of weird intermittent codes from corroded grounds there.
Injectors rarely fail intermittently on those ...bet you have a bad wire somewhere.
In reply to vdubinsd:
Yes it is running like crap, and really smells like gas out the exhaust. I'll start checking the wiring and also vacuum lines as I've read that could also be the culprit.
I did have the interior detailed right before this happened. Could they have caused the problem by hitting something inside the car?
Doubt it.
Engine detail....yes.
I don't know much about these cars but I would test the coil and make sure it is with in spec.
Good call...some of the early versions had a bulletin for adding a ground to the coil-only for certain engine codes...
would be more suspect if had P0300 codes also
I don't remember diddly about 2.0s, but I'll throw a hat in the ring for valve adjustment, also.
ValuePack wrote: I don't remember diddly about 2.0s, but I'll throw a hat in the ring for valve adjustment, also.
Does not apply here.
99 new body style or old body style (mk4 or mk3).
Individual coils or one coil pack dowe on front of engine?
Checked for vacuum leaks? Notorious for vacuum lines drying up and shrinking pulling them off connections. Especially at fuel pressure regulator.
If it smells like gas from the tailpipe I would look more towards fuel management rather than ignition system (assuming all the ignition parts were replaced with good ones).
The ECT sensor could definitely cause a rich condition, but you replaced that. If you still have access to a scantool you should check fuel trims and MAF flow values.
Long and short term fuel trims should be less than 10%. MAF should be flowing between -
2.3-2.5 g/s at idle (warm)
10-11 g/s at 2500 RPM (less tahn 9 is bad)
110-120 g/s at WOT at 25 MPH (in 3rd)
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