My 2 cents.
Fuel dist., injectors and possible coil....all 3 ???? Sounds to me like they're guessing - throwing parts at it.
There is a cold start valve on this vehicle. Could be an issue in the cold weather you describe. Check archives here.
You mentioned plat plugs. If you still have 'um, get rid of them and use Bosch spark plug H9DC0. There's also an H9DC, but it's electrode is not as wide as the H9DC0. These cars idle better on the plain copper plug.
MB says to gap at .032(that's what it converts to). Some say to go as high as .040. I set mine in the middle of this -> .036.