Have you removed the throttle body and throughly cleaned it with carb cleaner- paying particular attention to the edges of the plate? If not do so. You can not really clean them properly while they are on the car. A toothbrush helps. Don't hold the throttle body in a position that allows the carb cleaner to run down the rod the plate pivots on in the direction of the electronics connection. When they gum up (more likely to occur as they "mature") the buildup restricts the air flow at idle.

Randy