Any small foreign object dropped in the throttle can cause the idle to increase really high. My experience was on my 1987 Accord it had a carb. One day I was removing the screen that sits on top of the carb I guess it was an extra filteration but one of the tiny pieces from the sceen fell in the carb and it later caused my car to idle really high up to 4000 rpm. Currently I drive a 96 Contour 2.5 V6 atx and I like my car bought it brand new in 1996.
