Induction air will have little to no effect on the combustion chamber as
concerning the burn temperatures for nox creation.  Depending on year of the
vanagon (AC vs WB) there is an EGR but it is usually nonfunctional from
holes in the system from corrosion.

Too lean will increase some nox and off timing will really increase nox.
For fun find a shop with the old style emissions testing equip and hook up.
Rotate the dizzie just a little bit one way and then the other and watch
what happens to your readings for nox and hc. When timing is right both will
be at a good pass reading (your mixture may have to be adjusted a tweak if
you don�t have an O2 system) if your everything else is in good repair.
Ie filters, cat, wires, plugs, oil.  All the little things that should be
checked or changed before testing.
jimt
On 9/9/05 7:53 AM, "Doug in Calif" <vanagon@ASTOUND.NET> wrote:

> Dennis,
> Its my understanding after discussing with my mechanic that the outside air
> temp may make a large difference on the NOx when you take your vanagon in
> for smog check.
> A 100 degree day vs. say a 30 degree day.
> 
> Doug
> 
> 
> ----- Original Message -----
> From: "Dennis Haynes" <dhaynes@OPTONLINE.NET>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Friday, September 09, 2005 5:50 AM
> Subject: Re: NOx high
> 
> 
>> NOx is caused by excessively high combustion temperatures. Usual causes
>> are a lean fuel mixture or over advanced ignition timing. Since the
>> Vanagon does not use EGR, the engine settings are extremely critical.
>> The Cat has the major job of reducing the NOx and all aftermarket cats
>> do not have as much active material as the original so they do not last
>> that long.
>> 
>> Dennis
>> 
>> -----Original Message-----
>> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
>> Of Mike Miller
>> Sent: Friday, September 09, 2005 12:09 AM
>> To: vanagon@GERRY.VANAGON.COM
>> Subject: NOx high
>> 
>> Vanners,
>> 
>> My van passed smog but the NOx was just below the maximum. New cat two
>> years
>> ago.
>> 
>> Any likely causes to look at?
>> 
>> TIA
>> 
>> Mike
> 
>