Question about 1991 Honda Prelude

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Rising and falling idle

1991 prelude si... 2.1L...190k miles...the engine revs up and down while in neutral and in gear (manual trans).

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  • Anonymous Jan 12, 2009

    I checked the ECU and the LED shows 14 short signals. Is this code 14?, because the manual says it should show 1 long and 4 short, or is the computer malfunctioning?


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  • 91 Answers

Hey, first i would check all of your vacuum hoses. Over time they can crack and leak and that can create the problem, then the computer compensates to correct it. The throttle position sensor could also be a possibility and in combination with a vac leak, can create a wide variety of symptoms that are difficult to separate and trace down. Get a can of carb cleaner with the little spray straw, start the engine and let it idle to warm up. Spray a little on each vac connector, around the base of each injector or the throttle body, and see if the rpms run up. If so, you may have found a leak that needs tightening down. Vacuum hoses can sometimes just have the split end cut off and reconnected. The hard plastic spaghetti lines may be so brittle they need to be completely replaced. Manifold and throttle body bolts can be tightened up, but occasionally the gasket may need replacing. I would start with that and see what it does for you. Let me know if I can be of any more assistance.

Posted on Dec 08, 2008

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