[SoCal LS-L]

Just another thought on the matter of misfiring, if it IS a misfire......

If the TPS is telling the ECU it should be in idle mode, which would have the IAC valve open..... then he steps on the throttle..... if the TPS is faulty the ECU would not know to advance timing AND would make the engine run lean since the IAC would not shut until the TPS returned a voltage indicating the throttle is pressed. That would cause his hesitation AND a misfire, and could also explain an O2 code.