My 93 Accord has about 280K miles on it. Runs great. Looks great. Except at idle. Its recently started idling extremely high on occasion. Sometimes after a drive, when put into 'Park', the engine will rev up to about 2000 RPMs and then die off to 500 or so, then rev up to about 2000, then back to 500 again. It repeats this process but never dies. I've also noticed that the air intake seems to be sucking alot more air than it used to... to the point that you can hear it while inside the car. I was thinking it could be the IAC valve causing the idle problem, but I'm not sure of the symptoms when the IAC starts to go bad. Any ideas?

 

Your IACV may just need cleaning. There is a little screen in the IACV that gets clogged over time. If it's never been cleaned in 280K miles it certainly needs to be done. Pull the IACV off and blow that sucker out with some carb cleaner. I cleaned mine a few months ago and it idles great.

 

or replace it for 10 bucks at a junk yard

 

i had the same problem with my 91 accord and i replaced the IACV and it fixed it. so i would try either cleaning or replacing it.