Falling Flat 91 4.0 liter Laredo

A real head scratcher: After i start the enigne (cold) and put it into gear, it falls flat on its face. However, if i let it warm up in idle, everything is fine. After driving it, let's say, to the grocery store, i come back and it starts just fine (warm).

I have done various things - new wires, plugs, rotar, cap, cleaned throttle body, replaced idle air motor and now i am at a dead end.

Rather than Forest Gumbing my way any further, I was wondering if anyone else has had the same problem, and if so, what did you do to remedy the problem.

Thanks for the help!!!