Q: stall in engine ,i replaced the spark plugs but still missing when idling . you on 1996 Mercury Grand Marquis

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you can feel it when driving it
(1) Answer
To assure understanding of what you are saying - With engine running in Neutral or Park, you can hear the engine 'missing'??? (Running rough and wants to stall????) - 'A Miss' in the ignition/running engine is defined as a 'constant audible and rhythmatic GAP or SPACE in the engine firing'... As opposed to coughing or gagging or other sounds like sputtering etc. (which are in themselves indicative of poor fuel or carb/injectors as well as vacuum and other problem arenas). If the problem is truly 'a miss', then either we continue to 'shotgun it' with replacing the wires/harness, distibutor/reluctor, etc.... Or we can try to troubleshoot further. - I would try taking one sparkplug wire at a time off and then starting/running the engine to see if there is one of the wires that makes no difference in the symptoms when it is left unplugged with the others all in place??? Which would at least isolate it to which cylinder is 'missing'... Assuming one of the wires does not alter the symptoms (cylinder identified); with the engine off and the key in your pocket, remove the spark plug wire in question from the vehicle (NOTE THE ROUTING FOR RE-INSERTION) and inspect it for wear, cracks, carbonized contacts at either end or their mating surfaces (distributor/plug), etc.... if no obvious defects either swap it with another wire similiar in length (repeating the process of trying to start and run engine with one of the two wires now involved disconnected at a time... if there is no change in sound and symptom; then the problem maybe a chipped tooth on the reluctor/emitter (distributor) assembly (you need to inspect visually) or the problem is not electrical but mechanical and there is a bad cylinder compression, timing, or wear problem. Good Luck