1995 Buick Skylark

This car strarts up real good. But, when it comes down off of fast idle it wants to spit and sputter and try to stall out for a few seconds. Once it is done throwing it's fit it will run and drive like a new car. It has the 2.3L quad 4 engine. I have replaced the fuel filter, coolant temp sensor, fuel pressure reg, plugs, plug boots, coils, coil housing and oil pressure sending unit. Noting seems to fix it. If the heater is on when you start it, it seems to be worse then when it is shut off. Also the electric fan will not turn on. Anyone have any Ideas? Thanks for any help.
Rodney025