I have Automatic car.. (i Know i need a 5speed) But my problem is that when im traveling around at a higher speed like 25-40 MPH then i let off the gas it like 30 seconds to go back to 1500 RPM.. my car never use to do that. Like it will stay at 3500-4000 RPMs for a while..

i have replaced my spark plugs, and wires, and caps and it doesnt fix this..
i was thinkin its the tranny but the car only has 120,000 KM on it

any help would be great... Thanks In advance

 

RPM's should stay up for a while to prevent stalling. It is called a high speed idle. The ECU will add RPM's to idle until the car goes below a certain speed (Normally 15mph).