82 Vanagon Westy. 89K on original engine.

Took it to a local garage that is certified to smog test vehicles up for the
CA biennial inspections. Drove it for a about 2 hours prior so it was good
and warmed-up.

I passed all aspects of the test but the CO% at idle -- I was at 5.56%, with
a maximum allowable of 2.00. The CO% at 2500 RPM measurement was fine, about
0.62%.

So what could help? I'll be changing the oil and filter, installing new
plugs, cap, rotor, and points before the next check, but any ideas on how I
can lower the CO percentage? Could the AFM be at fault? Leaky injector
seals?

TIA ...