I just bought a new CO analyser so I could set my many VWs to maximum
fuel setting with the price of gas what is forecasted to be.  I
played a little bit with it this morning and am planning to get
serious about it on Sunday.  Initially, I found that the 2500 rpm
range was just fine (.7%, richer than factory setting but promoting a
cooler engine).  My problem is that I couldn't get the idle setting
under 1.2% by adjusting either the AFM idle mixture screw or the idle
setting.  That's at a stock factory idle setting of 875 RPM.  At 1100
rpm it would get close to 1.0%.  When I tried to starve it by holding
back the swing arm on the AFM, I still couldn't get it to lean out
(at least CO out).

I haven't pulled the plugs yet to check for bad spark but I don't
think that's it because they are fairly new spit fires.  Another
thought is that the AFM idle bypass passage is dirty and restricting
enough air flow at idle rich is making it richer.  This would explain
the idle  mixture being off and the 2500 rpm being OK.

I've wondered about a bad cold start valve, but a 2.1 doesn't have
one.   My overall mileage was down this winter until I replaced the
thermostat.  I still wonder if the temp II sensor is a little on the
slow or low side as it still is a little slow to warm up.  My overall
mileage right now is a little  over 20 MPG (mainly city driving, it
drops like a rock at and over 4000 rpm).

Any suggestions as to other things to look at?
--
Steve Blackham
Centerville, Utah

77 transporter converted to camper (Westy top)
83 Vanagon  (New and current project)
87 Weekender