Symptoms: When left overnight engine off, followed by cool/cold weather the following morning: The engine starts right away as it should. But, it chugs and sputters, if you will, until the cold start cycle is complete some 30 seconds or more later. Then runs fine.
Did the drip test on the cold start valve, not leaking by. The auxiliary air valve is obviously cycling off per the approximate 30 second timeout. The thermo time switch is obviously working as the car starts (actuates the cold start valve), and doesn't run rich after the approximate 30 second timeout. Idle speed is around 900 rpm. Differential pressure regulator current is approximately 10 mA.
88VW Fox, 1.8L, CIS-E. Going by the Bentley manual.