98 taurus misfiring and tachometer acting weird

My 98 Taurus started misfiring and Idling rough when stopped in park and reverse. Also Tachometer is intermittently dropping to zero when engine is running. These symptoms appeared right after I took the car
to the dealer for a 100k mile spark plug change and transmission flush. Also got a new fuel filter so it aint that. I pulled the plugs and they all had a light cocoa colored coating on them except the one at the rear on the passenger side. It was dark and didn't look oily, just no coating like the others. My next planned step was to shotgun it with new plug wires and and a coil module.
I don't want to go back to the dealer again, seems like they are just guessing like me most of the time but charging $$$$ for labor and high markup parts anyway.
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Most likely the plug wire. Being that its got 100K on it, it sure wont hurt .
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Since your car is OBD II, any garage can hook up the computer diagnostics and it will tell you which cylinder is misfiring. There is an amazing amount of info available from your car. I've used it to diagnose exactly which plug wire is bad. Try it.
Patrick

hurt
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Actually | have bought a OBD II to serial converter ic with Ford specific format from ELM electronics and am awaiting for a specific frequency crystal to be able to build a reader with it. I'm better at electronics than mechanics.
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