Honda Prelude Forum - PreludeDriver.com

I have an 87 si. Starts fine but idles around 500. Does not matter what you turn on a/c , lights, etc it stays right aorund 400-500. Does not cut off and you can put it in drive and go. If you let it sit and warm up some it will go back to 750 and idle there the rest of the time sitting or driving and you can turn on whatever you want it stays the same. You can pull off a vac. line and it will idle up. I am not sure what to do from here. I was going to try to set the idle by the book, but when you get to that point of it warming up it is at the correct idle. Temp outside was 72 today. Any thoughts?

Even though it starts to idle fine once the car is warm, I would still suggest that you go through the idle adjustment steps detailed in the service manual (see our manuals section). This will help you to establish a baseline.

Also, is your car throwing any check engine light error codes. If certain sensors are malfunctioning it will have adverse affects on your idle. The engine trouble light in your gauge cluster will illuminate if your ECU is reporting an error condition.

Ok, I will go by the manual and make sure it is set from there. I did today clean the throttle body and take off the IAC and cleaned it. Some carbon build up. No codes on the PCM and no pgm-fi light on the dash. I will set everything tomorrow and see what happens.

Awesome. Keep us updated.

Set the idle today per manual. It seemed to idle better but I will check again tomorrow when it is a completely cold start. According to the Honda manual if it does not improve then the IAC should be replaced.

A bad IAC will often result in a bouncing idle. If you're experiencing that, let us know and we'll give you tips on how to fix it.

Adjusted the ide. On a cold start it will idle up for a 5 or so seconds, then drop down to the correct idle (about 750). I know this should be a longer high idle on a cold start. I runs and drives fine cold or warm, no bouncing idle. I have a 91 and it will idle at 1200 or so for a minute or two before gradually coming down. On another note putting in a radiator on a 87 is not any fun.

Yeah, I would have expected it to high idle longer as well. Perhaps your IAC is defective, but you're not really going to hurt anything leaving it the way it is. The engine just won't warm quite as quickly.

Thanks for your help. I will wait till the end of summer before replacing it, since it warms up good in this warm weather without any problems.

Replaced the IAC valve this past weekend, cured the problem. Not to expensive $65 at Oreilly's and was in stock.

Awesome! And thanks for coming back to fill us in on the resolution; doing so really helps other people.