First thing to check is the throttle position switch, see Bentley p. 24-58.  Use an ohmmeter. If that's good look for vacuum leaks & bad wires or plugs, then check fuel pressure, timing, and the AFM per Bentley p. 24-57.  When I had this problem it was a bad injector or injectors.  Get them rebuilt, runs about $25 each from Rock Auto and others.

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Richard Koller
Sent: Thursday, April 30, 2015 3:02 PM
To: vanagon@GERRY.VANAGON.COM
Subject: vanagon stumble

Hi all,
My '91 tintop syncro has developed a stumble on initial acceleration. It hiccups a bit in first gear and then briefly hiccups more violently after shifting to 2nd and accelerating. It stops this stumble after gaining speed and shifting to 3rd. Also, if I decelerate or coast a bit and resume acceleration the stumble seems to happen just a little bit but goes away after further acceleration. There are no stumbles or misses during cruising speeds only at low speed shifting speeds. No idling issues or hard starting but it seems to have gotten worse lately, it was very rare up until this week.
Any theories.
Thanks
Rick