I thought the list would like to see an email I got and my responce
 I am asked about this all the time
Bernie  wrote:
>
> HI, I like your web site and it has proved to be very informative. I'm
> wondering if you could clarify how to set the timing on my 91 vanagon.
> The Bentley book kind of confuses me. I only have a regular strobe
> type timing light. Do I set the mark on the pulley to the crankcase
> edge at idle speed (850)  or at 2500rpm with the temp sensor
> disconnected?

the timing is set at 850 with the temp sensor connceted

When I connect my rpm meter to the coil I get a very
> erratic reading. Is this normal or should it be nice and smooth like
> it is when doing an air-cooled engine. If it is suppose to be smooth
> what would this erratic reading indicate.

 if the tach on the dash is steady then its ok

 The van seems to drive fine
> but the idle is terrible. When it's cold it idles very low, when it's
> warm it idles high, if I give the gas a quick kick the idle will drop
> to normal. Any ideas? The idle stabilizer doesn't seem to hum. What
> voltage should I get going to the stabilizer? What symptoms would a
> defective Oxygen sensor give? Thanks for your time.

the thottle switch tells the electronic control unit that the engine is
at idle if the throttle switch is not working, misadjusted or has
resistance then the o2 sensor does not go into the closed loop and that
richens the idle mixture and the engine has an eratic idle
another symptom of a bad throttle switch is that distributor timing mark
will do the dance when trying to time the dist

all this happens because the ECU thinks the engine is not idling

I recomend starting with a fresh ECU temp sensor 025 906 041 A
next test the 02 sensor and see how quickly the voltage changes if its
slow the 02 sensor needs to be replaced make sure the engine is fully
warmed up and the radiator fan has cycled twice before you set the specs

Bob Donalds
http://www.bostonengine.com