I have a 99 galant which has an rpm needle problem.

the check engine light appears once the rpm/idling gauge starts to spin uncontrollably. Once that occurs the car begins to lose power, shake and not want to acccellerate. I also change both coils.

The engine starts to misfire only when i turn on the heater. It is very weird.

A diagnostic is needed to resolve the problem........has anyone replaced the radio or installed alarm, made any changes electronically?