My 1990 240DL suddenly developed idle control issues. It stumbles and stalls during cold starts, and has loss of power/driveability issues until warmed up.

I'm using Bentley to trouble-shoot and have done the following:
-Ran diagnostic control function #1: No fault codes detected (1-1-1 reading)
-Ran diagnostic control function #2. Steps 1-10 had nominal readings, but step 11 (holding brake and changing gears on the AT) was abnormal (the LED just kept flashing rapidly).

Based on those results it seems that I have an idle control issue according to the book (thanks Bentley! Like I didn't know that).

Besides running the diagnostic tests I have:
-Checked the throttle control switch (ok)
-Sprayed the injector seals to check for leaks. Fluid stays around base of injectors for a while before it (I assume) evaporates. So I think those are good
-Checked for vacuum hoses loose or cracked (haven't found any)
-Inspected the throttle control valve (there was a little oily gunk in the body but didn't really seem that bad.

On my list of things to check I now have:
-Air Control Valve
-EGR Valve
-Transfer fuel pump operational?
-Air Mass Meter
-Coolant temp sensor (or an I assume this is good since no engine codes??)
-Test fuel pressure (saving this one for last)
-Test oxygen sensor
-Look some more for broken wires/connectors
-Look for bad ground wires
-Check the ECU

I'd appreciate any advice on which are most likely to be the culprit and which order to tackle these in.

Thanks in advance!