My car idles rough (chugging) after sitting for a while (overnight or a few hours). Revving it a couple times or driving around the block results in it idling fine thereafter. Recently I've even been having trouble getting the car to start. No visible smoke or noticeable loss of power. I dropped some fuel system cleaner in it today and will see how that works. Any ideas? Kinda sounds like a blocked fuel line/injector but I dunno.