CAR BUCKS AT LOW SPEEDS

I would probably suspect ignition failure of some sort. As you put load on the engine one of the ignition coils may be failing. Remove the ignition coils and inspect for signs of arcing or break down of insulation. Perhaps you may even find a bad wiring connection on the grey electrical socket at the top of each coil. Remove the spark plugs and inspect. Are each of them the same color, replace them if required. Remove the air duct from each throttle housing and clean the throttle housings with Chemtool or equivalent product. The fuel filter is easy to change and may be a good time to change that as well.

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