Volkswagen: 76 beetle fuel injection, rubber elbow, saran wrap

Question
engine always starts immediately but will not fast idle on cold unless accelerator is held for approx 30-45 seconds and then it idles very low rpm.  speeds up after driving a block or so.  i can drive for 10+ miles, cut the ignition and less than a few minutes later it does the same thing as when it is overnight cold.  also when engine is hot and comes to a stop light it idles very fast and then after approx. 30 seconds it idles down to a normal idle.  don't know is this is a related problem. have taken it to two "vw specialists" but they have no way to check the electronics since no one in my area has the equipment to do so.  both are baffled by this situation.

Answer

Aux_air_reg_78Bug I believe it's the Auxiliary Air Regulator.  It is located almost directly under the alternator.  It has an intake hose(the original is fabric covered) which enters on the right side of the regulator, and an output hose which exits to the left.  To test it:

1) Make sure engine is off and cold.
2) Disconnect the intake hose where it connects at the large rubber elbow duct (to the left of the air box), not at the regulator itself.
3) Start the engine.  It should idle fast.
4) Feel for vacuum at the disconnected hose (not the elbow connection itself.)  
5) If you do not feel vacuum immediately, the regulator is likely stuck closed.  If your finger is not sensitive enough, wave a small piece of Saran Wrap in front of the hose to detect the suction(but not small enough to get sucked in!)
6) If vacuum is good, when you completely cover the input hose, the engine should slow down, and maybe even stall if it's still too cold.  This is normal.
7) After a few minutes, once the engine is warm, the vacuum should stop (the valve has closed).  If not, either a) the valve is stuck open , b) the internal heater element is bad, or ) the battery voltage on the electrical connector is missing.

For #5, #7a of #7b, replace the regulator.   For #7c, you need to troubleshoot the electrical connection.   Of course, don't forget to check that all hoses are in good shape; a bad/leaky output hose could cause your symptoms.  Good luck and let me know what you find.

Additional info:
I realized that Temp Sensor #2 could be at fault also.  It is on the left cylinder head by #4 cylinder.  Check the electrical connection, it could be loose/dirty.  Also, test the resistance (cold) from the connector to ground, it should be around 2500 ohms.