Rough fluctuating idle when cold, high when hot.

Third Generation Honda Prelude topics

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Lude Dude
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Rough fluctuating idle when cold, high when hot.

Postby ns_wrestler130 » Mon Oct 14, 2013 6:34 pm

I have a 90 Prelude Si with the B21A1, the motor was just rebuilt and is not running well. I can not take it back to the mechanic that did the work as I moved from California to Texas. The car drives fine and seems to have plenty of power but upon initial starting the idle is very rough and fluctuates from the point of almost stalling up to about 1500 RPM's. When the car gets up to operating temperature the idle is around 2000 RPM's. No codes are flashing and I am a bit at a loss. The coolant is bled properly. I was going to pull off the IACV and clean it but before I did I wanted to see if anyone had other input on what else I should check while I am already under the hood. This car has been a long process and I can't wait to get the finishing touches complete. Thank you in advance for any and all help that can be provided.

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Joined: Fri Nov 11, 2005 2:55 am
Prelude Model: 1991 SE-SR
Location: Alberta, Canada

Re: Rough fluctuating idle when cold, high when hot.

Postby spiffyguido » Wed Oct 16, 2013 8:25 am

9 times out of 10 in my experience Hondas with a bouncing idle stem from a bad IACV valve. Start there. See here:


There are other things that can be checked, but you should rule out trouble with the IACV first.

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