Where I was living at the time, in the Canadian Maritimes, gasoline quality - even among the so-called 'top tier' brands - was often questionable.  We also had an early variant of the ethanol-enhanced gasoline in the market there, which was often blamed for the problem. European Car Magazine, back when it was called VW Magazine, regularly had items on this issue - and the local VW dealers stocked the Techron additive (which was otherwise unavailable in Canada).

Certainly the before and after effects of a dose of Techron on my Rabbit's cold engine idle on a cold January morning were noticeable.

James

> From: psdooley@verizon.net
> To: jk_eaton@HOTMAIL.COM
> Subject: RE: Removing stuck O2 sensor
> Date: Wed, 4 Feb 2015 15:38:20 -0500
> 
> That's weird, I drove CIS VW's for years and never had that problem.
> 
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> James
> Sent: Tuesday, February 03, 2015 10:21 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Removing stuck O2 sensor
> 
> A low or stumbling idle when cold that clears up when the engine is warm
> (and is not the O2 sensor) is nearly always carbon on the intake valves in
> VW engines - I've had this in CIS, Digifant and far more modern engines.
> Seafoam or other intake valve cleaners will make a big difference in a
> hurry.
> 
> VW engines are infamous for carboned intake valves - in the glory days of
> the CIS system, we were advised to run Chevron's Techron intake valve
> cleaner through every 5000 km or more often.
> 
>  
>