from my experience, EGR valves usually go bad when the motor gets older is when it happens. Maybe 100k-150k miles. I'm sure there are many factors that could change that estimate though. Cleaning the valve with carb-cleaner is a temporary fix. I've tried that a few times in the past and it usually only helps anywhere from a few hours to a couple of days at best.

I would recommend www.slhondaparts.com if you need a cheap source for Honda OE parts. They also have all schematics online for viewing. Its a SUPER easy install though. I can change it on my Prelude in about 3 minutes with a 1/4" socket wrench, extension, and 12MM socket. Far as I know, ALL Honda EGR valves come with the new gasket too.

Good luck with it!

brad