i have a 1991 honda accord and it does that up and down idleing, and i took it off to clean it and it looks pretty damn clean, but i filled it up with brake cleaner, and now it has gotten a little better with the idleing, but it still does the up and down idleing. maybe i just need to replace the IAC itself. i looked on the internet and it was about $47. if anyone can find one cheaper or has one for sale, that would be awosme. thanks everyone.

 

check all your vacuum lines for leaks (especially the one to the IACV), could be a vacuum leak.

 

Use factory part from honda. Important.