high idle, stumble when hot!?!?

i have a 96 xj sport, it idles around 1750. and i acts like it has a miss. it stumbles upon take off only after it sits about an hour or so and only does it the first time. it had a intake gasket leaking and i fixed it today. new plugs, wires, cap, and rotor. and nothing has changed. it had 2 ecm codes in it, correct idle not achived, voltage to low. the stumble is at about 2000 rpm it just falls on its face for about 2 seconds and then takes off and go, only in first gear and only once after starting when left sitting for an hour or so. can anyone help on this, i cannot figure this one out. i also cleaned the throttle body and check the timming.

timing is not adjustable, so there is nothing to check. you could have an o2 sensor starting to go out