I have a 99 galant which has an rpm needle problem. on 1999 Mitsubishi Galant

I just had my timing belt and crankshaft sensor replaced. Car runs fine but once i turn on the heater the cars rpm/idle needle starts moving uncontrollably and the car start to misfire by shaking and not wanting to accellerate. The check engine light also goes on but i had the light check and it says it needs a tuneup which i already did with new parts. I dont know what to do.

Asked by for the 1999 Mitsubishi Galant
you need to resolve the light issue which is telling you about a missfire. start with a compression test to see if there is any valve damage.

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.
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I want to make sure I understand.....the engine misfires only when you turn on the heater?......or the misfire becomes worst when you turn on the heat?
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?