I have a similar problem with my 16V, 1986, 155k miles.
Starting is OK, but when cold outside (almost winter here in Colorado) the idle speed is very low, 500-700 so the engine stalls easily, especially when engaging in Drive (which will reduce the already low idle.) In the summer, the idle was fine, around 1100.
All fuel related parts are new as is the O2 sensor.
I am suspecting, as RCMKTG and MBDoc suggested, that the Air Flow sensor potentiometer is bad.
Question: Anyone knows a source for a new one? I have checked around and the best price was $420 (ouch.)
Regarding the AirFlow sensor, I did check check the potentiometer (while disconnected from harness) and slowly moved the plunger up/down. I found the readings to be erratic, espacially in certain positions. My mechanic (MB independent whom I trust) told me that his test showed that the sensor is OK.
While I respect his expertise and based on my own measurement,
I tend to think that the part is worn out (and why not, after 155k miles).
Any thoughts greatly appreciated. Pat, if you are reading, you mentioned having a similar problem. Maybe we can get a few people together for a group buy?
THanks All, this is a wonderful forum and resource!!!