Is it a "miss" or uneven idle? On the Waterboxer misses at idle usually indicate a balance problem. The cylinders are not getting the same air and fuel delivery. Above idle there is much more tolerance. You can have a bad injector, vacuum leak, or an engine problem. Intake valve issues are very common. You  can discount the O2 sensor and with the engine running ground the sensor input lead briefly. This will cause the system to enriched the mixture. If this helps then most likely you are dealing with what we call a "lean" miss fire. One cylinder too lean so the fuel doesn't ignite.  This unburned fuel can make the exhaust smell rich causing more confusion. 
 
Dennis

 
> Date: Fri, 13 May 2016 08:24:47 -0700
> From: tyler@SERAPH-NET.NET
> Subject: Miss at idle?
> To: vanagon@GERRY.VANAGON.COM
> 
> Where to start?
> 
> Distributor cap and rotor, plugs are < 500 miles old.
> 
> Wires are < 1 year old (Bosch from Van-Cafe)
> 
> Timing was done 6 months ago with a light at idle. I checked advance at
> that time and it seems to work. P.O. had marked the main pully with white
> paint.
> 
> Yes, I lubricated the felt. :-)
> 
> Temp 2 sensor is < 1 year old
> 
> Probably easier to start a list of what I haven't done:
> 
> Hall Sensor..
> Coil..
> Fuel Injectors..
> Idle Stabilizer Module..
> 
> I know that I need to adjust the throttle body micro switch. I've just been
> lazy..
> 
> Anything else I should be looking at before I throw money at it?