Engine RPM

I have 2002 Mitsubishi Eclipse with ~105K miles on it. I bought it 3 months ago. It has a strange problem. The RPM starts to drop, whenever I stop at signals or stop signs, or stop for any other reason. It comes back to normal when I turn off the fan. I am not sure what is going on.

Have your battery and charging system tested. Most auto parts will test for free.

Also, make sure the cable connections at the battery are clean and tight. Same goes for the connections at the other end of the cables.

thanks a lot. I’ll do that.

Its not really all that odd. As mcparadise suggests you should have your charging system checked. Any the things you turn on (or the car turns on such as the cooling fan for the radiator) draw power. If your alternator and/or battery or the connections are in marginal condition that draw puts extra load on the engine.

The other stuff to do is make sure all basic maintenance items are up to date. Spark plugs, wires, fuel & air filters at minimum.

When you turn off the fan? Do you mean the A/C? If it is the A/C your ac compressor may be getting hard to spin applying too much resistance to the engine thus lowering your rpms. Please define “when I turn off the fan”

Thanks for the reply. AC is not running, but the heating is (as you would imagine for winters in Buffalo, NY). I don’t think compressor should be running if AC is off.

Thanks for the response. It does make sense.

If you are using the “defrost” setting on the HVAC system, your A/C compressor may be running, as that is the way that the system is designed to operate.