proper exhaust flow is essential. it can cause the car to run rough or putter depending on how bad the exhaust problem is and where it is. also, if the cat. converter is bad... your car is probably loud and the exaust is probably vibrating violently enough to make the car feel like it's running rougher than it really is.
point: yes, it could be the cause of the car running rough. but i'm sure there is more to it than that.
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