Damn this is the 3rd idling problem this year...I need help this is driving me crazy.

Idle problems this year and it's solution
1. Coil
2. MAF and O2 sensor
3. ??? (Car was running fine. I've been cutting down on my driving since gas prices have been creeping up. My car will sometimes sit in the garage for 3-4days before I take it out for a spin. Now my car has a stumbling problem at idle. Otherwise it's fine as long you're stepping on the gas. It starts fine. Idle is rough in all gears, but really bad in drive or reverse. I asked my mechanic and he said something about vapors being in the line...he wants me to take it in. Can this be the fuel pressure regulator? I'd like to try to solve this myself before taking it in. What are the signs of a failing fuel pressure regulator?)

The following have been replaced with new part...along with the 3 above
Spark plugs/wires/distributer/rotor
OVP
alternator
Temp sensor
Fuel pump/filter

__________________
JR
1986 Gold 300E 4Dr automatic