Recently bought, 150K miles, fair condition. When driving on city street, there is a momentary increase of RPM, let go of the gas, and returned to normal operation. Any idea?
Do you have an automatic or manual transmission? You say the RPM’s increase, does the speed of the car increase? Does it do this from a stop as well? Does it seem to do it as you are accelerating?
It sounds like your transmission (automatic) is downshifting when you accelerate, and then upshifts later. Do you have an automatic, and is this what is happening?
All cars do this, and if this is your situation, I would not worry about it.