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I have a 1991 Prelude Si with about 130k miles on it. When the car is idling in park or neutral the car idles at about 2000 rpm and revs up to about 3000 and drops off every couple of seconds until i put it in drive or reverse. It also does it in drive but not nearly as severe, but it is noticeable when breaking. Subsequently it is getting about 14mpg instead of my expected 25 mpg or so that it used to get. any ideas?