I bought a 01 Jetta GLS 2.0 4cyl 5spd not turbo I really like the car but I already replaced the starter and now (not even two weeks into this) in the mornings it runs REALLY rough, it's not that cold where I live (N.Carolina) maybe 50-55degrees in the mornings but it starts fine then I get on the road and it bumps, and sputters and changing gears and pushing the gas doesn't help it's like it just can't go today I had to pull over and let it rest then I went on and it was fine like nothing ever happened, what is wrong? did I buy a lemon? It's done similar things before but not to the point that I had to pull over. Please tell me what to check I have a VERY limited knowledge of cars so be specific, and don't just say take to a mechanic after the $300 starter that's all I need. Also the check engine light is on and the mechanic said it's the O2 sensor he said that may make the car sputter, but I thought the O2 sensor was just for emissions checking so who really cares if it works?
Beyond that, [and I recommend this to anyone having poor performance issues] try adding a bottle of Chevron's Techron Fuel System Cleaner, $6 at any parts store or Wal-Mart, with a few tanks of BP or Shell Premium fuel.
Lastly, if those things don't work, you may have a bad warm-up regulator - it's the little gizmo that makes the car run rich for a few minutes while it warms up...sort of like a "choke" on old cars or on your lawn mower. If it can't make the car run rich, it will be rough-running until it warms up. I've got a VW now that needs a warm-up regulator, but it doesn't bug me enough to fix it. Yours may need looking into if the tune & premium fuel doesn't correct your situation.
The reason your Check Engine light is on is because your car has recorded "misfires" in the cylinders. The light will go out eventually - don't sweat it. You didn't buy a lemon, more likely just got a car that was in need of a tune up and some good fuel run through it.
I'm in NC too. Feel free to Email me if you have any specific questions.
It may also be in need of Spark Plugs and Spark Plug Wires.
My guess is that the O2 sensor is bad and telling the ECU that the car is running too rich. So the ECU tries to lean out the fuel mixture. Normally not such a bad thing, but when the car is still cold it is like driving an old carburated car, cold, with no choke.
An O2 sensor cost around $70 plus installation. You could also stop by an Autozone or other big car parts place. I understand that they will read your error codes and be able to tell you why the computer is turning on the check engine light.
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