high idle and low rpms when braking

[Teamchicken]

hey guys, i have a 1993 JGC laredo(187k miles) with an I6 and whenever i have the car in park or neutral it idles at about 1500rpm and when i brake at a stop light the rpms go way down to about 100 and it idles rough till i am stopped for a second and then it does back up to normal. but when driving it seems pretty normal. any help would be appreciated
edit: also the check engine light comes on and off