engin starts fine and runs smooth until it starts to warm up, then it starts to stumble and gets progressively worse as the engine gets warmer. It sometimes will stall if in gear at a light or stop sign. It will start back up (sometimes with a little coaxing) but it seems to want to stall, sometimes catching itself for a few seconds. runs fine above idle. i removed and cleaned the idle control valve and cleaned up a couple of questionable vacumn lines but still does it. any help would be appreciated -