Engine problems in 99 honda civic.?

[mjm215]

I have a 99 honda civic ex auto 131k on it. My idle is very bad idles are 300 rpms and the whole car shakes. But lately, when im at a red light my car sputters and stalls, so now i have to hold down the brake and gas at the same time at every red light so the car doesnt stall. I replaced the sparks, and wires about 2k miles ago but i didnt touch the distributor but it looks ok. Another thing is when i have the heat on my idle is perfect at around 900 rpms and the car doesnt shake at all which i think is weird. I also replaced the fuel filter and had a new exhaust put on and the people at the exhaust place said my catalytic converter is fine. But the idle is still bad and the car is stalling, Another weird thing is the car runs perfect when its cold, but once its fully heated is when the problems start, and last night i was driving and suddenly my car started slowing down while i was holding down the gas pedal then it suddenly kicked in, it did that about 3 times, then i stopped outfront of my house and my idle dropped to about 50 rpms and the car was struggling to stay running and all the lights were flickering from dim to bright. Any help would be appreciated.