i have a mitsubishi outlander 2003. i don't know much about mechanics so i'm hoping someone could explain this problem to me in layman's terms. when the car is in park the engine sounds too high, the rpm gauge shows 1500. then it will drop down to about 800 rpm only to jump back up to 1500 rpm. it does this pretty consistently when in park.

what could be the problem??

 

It could be anything fuel/air related plus mechanical. It depends on particular design and control logic. I would suspect an uncontrolled air leak, so whenthe throttle is closed, some air still gets past it increasing the idle rpms. ECU cuts the fuel (as per algorithm's threshold)to decrease the rpms since it knows of the idle condition and/or closed throttle. Anything else you would figure from there. Try to analyse when/why/how this problem occured, maybe you will get a better idea of how to fix it.
Good luck troubleshooting.

 

Another thing to check is if this only happens when your A/C is on. When the A/C compressor kicks on it can raise your idle rpms.

 

I support azjake in opinion about A/C.

 

I'm not sure I fully understand what you are saying. does the RPM remain at 1500 constantly when in Park or does it jump up and down between 800 and 1500 RPM?