DEFECTIVE EGR VALVE IS THE PROBLEM : )
I have an 87 Bronco II with 2.9 V6. Was having same warm up and stammer and sputter with loss of power. I did everything - plugs, wires, IACV, TPS, etc.
Had hunch it was a defective EFR valve. Tested the problem by placing a metal plate (made from cutting up an aluminum pop can) between EGR valve and intake. This prevented any exhaust gas being able to be recirculated back into the intake improperly. VIOLA!! FIXED PROBLEM!!
Stupid EGR was stuck open and choking car with too much recirculated exhaust gas. This was making the car sputter due to lack of oxygen and the car' s computer was doing its best to compensate the proper fuel air mixture but just ended up running way too rich and stinky.
Good luck.