Hello all,
Have an 86 westy that has hunting idle - idle controller is varying the idle speed at a rate of 2-3 times a second. That is the speed goes up and down 2-3 times a second.  The actual idle speed only varies by 30-50 rpm - from 900 say to 950 rpm.  With throttle open slightly the hunting goes away.  Also the hunting does vary - sometimes the idle is stable at approx 925 rpm. 
Hunting happens when cold and when warmed up.

Checked the input to the idle controller at pin 17.  Not sure what I am getting  but I tried disconnecting pin 17, then the hunting goes away. Idles really smooth with no variation at all.  I thought the input to pin 17 was from the ignition coil pin 1 but I cannot get continuity with an ohmmeter.   My bentley is for  80-85 models so I don't have the 86 Bentley info.  I am working from a 84-88 Chilton FI manual that has a section on Digifant.
 Thought I would leave it with pin 17 disconnected but not sure on it's effect on emissions.  Vans i due for bi annual 'e-test' next month.

Can any one help with this problem?  Before I go crazy.
Just spent all day trying to solve but got nowhere.
Checked throttle switch - ok. Replaced Hall sender (it quit in the middle of all this).  Replaced dist cap and rotor.
 Thanks in advance.
John
Elora, Ontario.