Misfires under load (acceleration) can be caused by leaky spark plug boots. When a spark plug boot leaks, it allows the spark to arc, or jump, to the cylinder head. New spark plug wires will be needed.
Mazda MX-3 Problem Reports
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Vehicles with a V6 engine may develop an engine misfire under load (acceleration). This can be caused by a valve cover gasket leaking oil into a spark plug well, shorting the spark plug to the cylinder head. To repair this concern, the valve cover needs to be resealed and the spark plugs and wires should be replaced.