Hello everyone. I have spent hours searching for the answer to my question and have yet to find a decisive one. This will be a very detailed post, but since W124 idle problems are so common, complex, and elusive, I think you guys will need lots of info to help.

My car is idling very roughly. About 3/4 of the time, when I start the car and watch the tach, the rpms jump like they used to, but instead of stabilizing at around 800, the car immediately dies. If I give it gas and rev it up once or twice, it sits at around 500 rpms and the car shakes like crazy. When I accelerate, I will get some hesitation only when I accelerate somewhat hard (but not all the way to kick down).

From my research, the idle control valve sounds like the most viable culprit. THe mechanic that had the car for the last few days said that is the next thing he'd check. I took the car in because I BOMBED emissions (not even close), and I assumed it was related to the rough idle. Unforunately, it wasn't.

I am in a whiny mood, so I'm going to give you all my recent service history (last 2 yrs). I have given my beloved car so many chances and probably should've sent her to the junkyard long ago. Oh well.

-Fuel distributor replaced
-rear main seal replaced
-head gasket replaced
-valve job
-oxygen sensor replaced
-drive belt tensioner
-new motor mounts
-replaced all injectors
-BG44k fuel system cleaning
-Distributor Cap
-Rotor
-ignition coil
-crankshaft position sensor replaced
-hydro accumulator valve replaced (attaches to fuel distributor)

Other hints, since the mechanic made detailed notes:
-Check engine light is on, code is G312- "Oxygen sensor shorted to positive, MAS Fuel pump relay circuit 87 not functioning"

-they said "tested fuel delivery rate excellent at 1000ML at 60 PSI in 30 seconds.

-they said "idel control valuve appears faulty; causes sticking high idele. When unit is unplugged and then plugged in again to wiring harness, idle regains proper RPM".

My research says that the two most common culprits are the idle control valve and the Over Voltage Protection (OVP) replay.

For a complete newb who is sick of spending so much money (over $8k in repairs), is the idle control valve easy to replace?

Can anybody give other insights or potential problems?? I'm an inch away from sending this heep of ***** car to the junk yard.