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Danny
Danny, VW Mechanic
Category: VW
Satisfied Customers: 4004
Experience:  ASE Master Certified with L1 Certification, Volkswagen Certified, VW and Audi repair shop owner
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Jetta: 2.0L..misfires..P0303/P0304) when accelerating..highway speeds

Customer Question

98 2.0L Jetta (ABA) misfires (P0303/P0304) when accelerating up to highway speeds. Runs perfectly (no codes) if you stay below 45. New wires, plugs, coil, dist cap, rotor and MAF. Smooth idle. Suggestion?
Submitted: 8 years ago.
Category: VW
Expert:  Danny replied 8 years ago.
Dansmith,

Does the vehicle also lack power under heavy acceleration? Only 3 and 4 misfire never 2 or 1?

Danny
Customer: replied 8 years ago.
Yes, it lacks power under heavy acceleration -- I'd say that that's the primary cause of the misfire when getting up to highway speed. Once at speed it smoothes out. I just re-pulled the codes -- still just 3 & 4.
Expert:  Danny replied 8 years ago.
I think you have a plugged catalytic converter, this symptom is hard to diagnose, almost indistinguishable for even a dealer tech to diagnose from a faulty cap/rotor and often only misfires on a couple of cylinders.

Drop the exhaust pre cat, clear the codes, and take it for a drive. It'll be loud but my bet is you won't have the lack of power or misfires anymore. I'd say that's the problem.

Danny
Danny and other VW Specialists are ready to help you
Customer: replied 8 years ago.

I'll give it a shot. Thanks.

Expert:  Danny replied 8 years ago.
Let me know how it turns out.

Danny
Customer: replied 8 years ago.
I replaced the catalytic converter -- there is a definite increase in power. Unfortunately, I am still getting a misfire in cylinders 3&4 (P0303/P0304) with heavy acceleration. Any other thoughts?
Customer: replied 7 years ago.
I eplaced the catalytic converter -- there is a definite increase in power. Unfortunately, I am still getting a misfire in cylinders 3&4 (P0303/P0304) with heavy acceleration/going up hills. Any other thoughts?
Expert:  Danny replied 7 years ago.
I think it's time to do a compression test on the engine to see if it lacks compression on those two cylinders. If that turns out ok I'd swap the number 3 and 4 injectors to cylinders 1 and 2 and see if the misfire follows the injectors to 1 and 2.
Customer: replied 7 years ago.
OK. I'll give it a try this weekend. Thanks!