200 hyundai elantra rough idle

I have a 2000 hyundai elantra 140k with a intermittent rough idle. It runs fine under power but when I stop at a light or sometimes when it first starts up it idles rough. it doesn’t happen all the time and has gotten worse over the last 6 months. The car shows no codes and the check engine light is not on. I just changed the timing belt. plugs and wires have 15000 miles on them. milage seems a little low on the highway but not too bad. any ideas?

Also replace your fuel and air filters if they are even close to being due and pull and clean your idle air control valve & throttle body.

Thanks those are good ideas!