Fuel probelms When my 2004 chevy malibu is sitting in park can rev up to 4000 rpm but then bounces down to 3500 and fluxuates back and forth. How do i change the fuel filter. Have changes the oil and filter, air filter..any other suggestions?

Try hitting the brake off and on to see if the rpm changes when you do that with the car in park. If it does, you may have a ruptured brake booster. A fluctuating rpm while your car is in park with the brake on indicates a vacuum loss. Other things may cause a vacuum leak including the air conditioner controls inside the vehicle. Other things that cause this may be cruise control or your Air Conditioners high idle solenoid.

It is goverened to do this in park.