After a weekend away, got a chance to replace the fuel pressure regulator. I ended up getting a Bosch (same part number as the one I removed), turns out this parts is also used on many VW's of the same era. There seems to be some issues with the regular part suppliers about the right part number (exactly as Dom pointed out, threaded vs. nipple connections). I didn't want to go down that foxhole, so just got the right Bosch part number (0 280 160 235) which is a 3bar regulator by the way.
Put it in and the car runs (dare I say...) as it should. I fiddled around with the idle stop, and it doesn't seem to be too sensitive, I guess the IAC is simply compensating to get the right amount of air in there. Here is what I ended up doing : Found the point where the set screw comes in contact with the throttle (using a very thin feeler gauge is good for this), marked the point, then turned the screw CW (in) to see where TPS sensor trips open (bottom two pins, normally closed), found this point then turned the set screw back (CCW) to see when the TPS closes again. There is, of course some hysteresis in the switch. This is shown in the picture below.
The idle seems pretty insensitive to the position of the set screw, as long as it is between the first contact point and the point where the TPS opens. The idle does increase as soon as the TPS opens, and the idle does go down when the throttle is fully closed, but in between these two positions, i did not notice much difference, so I left it at the halfway point.
Can anyone confirm that the TPS open and close positions are more or less right?
The last thing I need to address is the evap solenoid not getting a good ground switch to come on, I think what I will do is just ground the neg side of the coil so that the solenoid comes on when the ignition is on since the 12V is supplied by the switched relay. I believe that the solenoid is always on with ignition unless it is cold, in which case it either waits for the coolant temp to get to a min value or uses some other trigger. Does anyone know the switching logic for the evap solenoid?
69 1750gtv / 73 2000spider / 91 Spider (daily driver)