I have been plagued with the infamous stumbling problem for several years
and believe I finally cured it. I tried all of the various suggestions
regarding temperature sensors, fuel injector cleaning, reseating
connectors, etc. Here's what finally isolated the problem and worked for me.

I was suspicious of distributor/hall sensor/coil for some time because the
problem seemed to disappear for a while when I replaced the hall sensor
last year. However, it soon returned. Also, I noticed that it was
associated with various degrees of erractic behavior of the tach. I finally
discovered some corrosion on the plug which connects at the side of the
distributor to the hall sensor. This plug has three tension contacts which
are not one of VW's engineering triumphs. Each contact is a u-shaped jaw
shaped and tensioned to be a tight fit when the opposing pin slides into
it. The pins in the opposing socket do not enter it longitudinally, but are
positioned so that the contacts fit over then sideways. My description may
not be clear, but you will see what I mean by taking a look at the connector.

The problem was that the tensioned contact was corroded and stressed,
thereby not making good contact. I cleaned the contact area with some 600
emery paper and retensioned it by carefully persuading it with a dental
probe. This fix lasted from last fall until a few months ago when the
humidity here increased after being dry for most of the summer. The
stumbling problem returned in spades, but disappeared immediately upon
application of another treatment. I suspect that the emery paper has
removed any plating remaining on the contact making it more susceptable to
corrosion in the future.

And, of course, this is a connector which cannot be obtained from the
dealer without being attached to a mega-dollar cable harness. If anyone has
any sources for this part, I would appreciate hearing. Thanks.

**********  John Clavin  |  jjc@bga.com  |  Austin, TX  **********