probably one cause would be no air filter mounting gasket, it's one gasket that gets misplaced a lot of times.

 

how would this cause an idle issue?

 

there is a hose that comes from top of valve cover to the back of the air filter box and thats how you get the build up....

 

Maybe because air that seeps in around the hat without a gasket is not filtered air, then add oily air from PCV = gunk buildup

not the only cause but one of many that may contribute to idle problems down the road.

 

I had the same problem and just replaced the IAC. It was only $40, and now I know I wont have to just clean it again in a week. Also put a new filter on w/ filter gasket. Also just put a filter on teh valve cover pipe so it doesnt go into the intake anymore. Hopefully it will keep the gunk away forever!!!. lol.