I did a search but haven't read a post w/symptoms that my car has.

Car starts and runs fine in the morning, but after it's warmed up it develops a low surging idle and hesitation on acceleration. Some times it's so bad it'll stall the car. Car will restart, but only after some difficulty.

Things I've changed (for new parts) previously for idle problems in the past.
2001
Rotors
Cap
Spark Plugs
Wires

2002
OVP

2003
alternator
Found a loose vacum hose

2004
Nothing

2005
fuel pump
fuel filter
temperature sensor
injectors cleaned
spark plugs
ignition coil
...new idle problem this year is frustrating me. I've already spent appprox $500. I'd hate to continue to throw parts at it randomly. What should I try next?
Oxygen sensor? (Has anyone tried the Ford replacement?)
Fuel pressure regulator?
MAS?
ICV?

Please help....

__________________
JR
1986 Gold 300E 4Dr automatic