Idle problems?

ive noticed only in idle the engine idles rough, when i put the car into drive its fine even at lights, what could cause the idle all of a sudden to go bad? the only 3 things ive done to the car is install a K&N filter to the stock airbox, PCV, and install a fuel filter, its an aftermarket one, think the filter is causeing the problem? The engine only has a little over 20k miles on it BTW
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Clean the idle air control motor located on the throttle body. This controls the air entering the engine and it gets carboned up quickly. Simply remove the screws holding it in place, spray it with carb. cleaner and allow it to dry. Once dry reinstall. One word of caution. Do not move the plunger while it is removed.

Clean the idle air control motor located on the throttle body. This controls the air entering the engine and it gets carboned up quickly. Simply remove the screws holding it in place, spray it with carb. cleaner and allow it to dry. Once dry reinstall. One word of caution. Do not move the plunger while it is removed.hopefully i can find that, thanks