Ok, a few months back I took my '04 Aveo LS Hatch to a mechanic for a new timing belt, water pump and serpentine belt. It was almost immediately after I got the car back that I noticed my idle was a bit rough and the car shuddered a bit when idling. The car drove fine except for the rough idle. I took it back to the mechanic a few weeks later and said my idle has been noticably rougher since the work. He looked at it again and told me I had a bad coil, which he replaced for free. I got it back again and the rough idle and shuddering are still there and just as before, the car drives completely fine except for the rough idle. I went ahead and changed the spark plugs - no difference.
The idle seems to be smoother when the engine is warm. It also seems to be smoother when the battery is disconnected for a long period of time. I haven't seen a strong correlation between the amount of gas in my tank and my idle. Every once in a while the idle is so bad that my RPMs jump a bit, from 800 to about 1200, but this isn't usually the case. Before the timing belt work my car idled around 800 RPM...it still idles around 800, its just rough.
Reading other threads it seems that the usual suspects are the IAT sensor and cracks in the vacuum tubes. Is the IAT sensor the one on the intake closest to the air box? Can anyone provide me the locations of the vacuum tubes? Or should I just assume that my timing belt job was botched? I guess I thought that the car would constantly run like crap if that were the case. Has anyone messed up their timing when changing their belt? How did the car run?
Any help is greatly appreciated.