I recently had a new engine put in a 98 Protege (1.5). The car had been sitting for a couple of years. It runs great most of the time. About once a week it will start bucking, surging and loses power. Usually if you stop for a few minutes it is fine. The check engine light has never come on. When my husband scanned it it said that the it needed a catalytic converter. Could this be the problem? I hate to start replacing things unless I know where to start!

Thanks!

 

Has the fuel filter been replaced? It almost sounds like a fuel pressure problem. Another thought is an EGR (Exhaust Gas Recirculation) valve that can be getting stuck open, this will be most noticeable when slowing down after driving at highway speeds.

If you scanned for codes and got the "catalytic converter efficiency" code, this will not cause this problem. If the converter is bad it will happen every time you drive the car, not intermittently.