When my wife and I were at BBTT, we used Karl Bloss's digitool during our road cruise to test the performance of our van. We were having a idle surging problem. By the end of that afternoon we were able to determine exactly what was misbehaving: the idle stabilizer valve.

With advice found in the archives, we were able to cure the problem completely. Of course, we now have a digitool of our own.

Larry and Avery Johnson
'86 Syncro Westfalia
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Björn wrote:

I am asking for some helpful thoughts or pointers on an intermittent idle
surge problem. I could not find anything conclusive in the archives, so here
it goes:

My 87 Syncro occasionally has a fast idle of about 2200 rpm. This is
happening during warm up phase and when engine is at operating temperature.
Also the engine occasionnally balks in the transition from deceleration to
acceleration (as the fast idle is pushing and the car is slowing).

I suspect the idle stabilizer, but since it is an item that costs more than
can$200 new and can$125 used, I want to be sure. The idle stabilizer is
humming but I do not have a CO tester to verify its operation. Since it is
happening in cold and warm operations I am excluding oxygen sensor and
coolant sensor. The complicating factor is also that the problem is
intermittent and it is raining and cold which dampens my enthusiasm about
any repairs.

What else could it be?
The airflow meter? (maybe but it would affect other rpms too)
the air temperature sensor?
the idle switch? (it probably needs adjustment but it should not couse surges)
the fuel shut off on deceleration? (possible)
The relays in front of the right rear light?

Give me some thoughtful pointers before I get my hands dirty.

Björn Ratjen