1987 Plymouth Horizon

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The importance of whether it comes through the intake or exhaust is important but the cheapest thing could be it needs a complete tune up because the cap is causing the plugs to spark when they should not. If its running too lean, valve timing, feedback carb. System, bad seating valves, also. A lot of age and mileage opens many possibilities. I hope its just a bad distributor cap. I used to drive that kind of car and 1 year later fuel injection was available and then gone. No more little spacious L body.