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Q:

reving up and down? on 1991 Acura Legend

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
my car revs up and down when in park but it only does it sometimes,what could it be and how much do you think it would cost to switch it?
(2) Answers
It is generally a cold idle valve problem. The Acura has a 2 piece idle valve, 1 part for cold running and 1 for after the car is warmed up. It is usually the cold running valve that sticks and then the idle goes up to about 1800 and then the computer will shut it down and then it goes up again, over and over. It is not that hard to replace the idle valve but the part is a hefty $300 or so.
I had this problem resolved by replacing the vacuum hose to the cold run valve. The hose is neglible, getting to it is another question.