The car has a rough idle and my tachometer dances around at will. I can be loafing at 30mph and the tach reads 5000 rpms.This in intermittent problem. I just drove across country, 1000 miles so the car runs fine at highway speed with only an occasional miss. New wires, cap and rotor were installed before the trip. The car only has 220000 miles on the odometer. Any ideas?

have you replaced all vac fittings & hoses?Maybe check all exhaust studs see if they broke off.Is the intake manifold gasket secure?is there a leak near the throttle plate??

The vacuum hoses seem good. The exhaust studs are intact and I already did a torque check on them as did with the intake manifold. I think that I will just disconnect the tach for now. I'm looking at another culprit, the coil.It was fairly hot after a short drive. I have never noticed that before. It is from a junked car and may be going bad as the last one did.

Good idea, check the power stage too. Look for wire corrosion and check ground cleanliness and condition. Wouldn’t hurt to do an electrical test on the coil, power stage and O2 sensor.
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Will I buy another Volvo??? We'll see....

I agree, check for vacuum/air leaks for the rough idle and missing. How is your gas mileage? Any OBD codes? O2 sensor okay?

Think the tach jumping around could be a separate problem. When you saw 5000 rpm at 30 mph I assume the engine wasn’t turning 5000 rpm. So perhaps the tach is electrical? Maybe a bad ground?

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Will I buy another Volvo??? We'll see....

Codes are 1-1-1 and the mileage is a bit down.