I've posted some questions about this before.

I have an '85 Vanagon with 135,000 miles on it.  It runs really well but the
idle and mixture adjustments are concerning me.  It barely passed its
emissions test this year and probably won't next year--I would prefer and
would feel better about driving this car if it were cleaner.  I have
attempted to adjust idle (idle stabilizer disconnected) and the idle control
screw has very little effect on the RPM.  I have also attempted to  lean the
CO adjustment down--this adjustment seems to make no difference in the way
the engine runs.  In other words, I could adjust the screw to where it was
at maximum lean and no effect on the engine's performance would be noted
EXCEPT that now when I let off the accelerator the idle does not return to
normal immediately -- 4-5 second delay -- Sometimes longer.

Anyway, I am assuming that the Air Flow Meter adjustments have little or no
effect  on this engine.  Do I need a new Air Flow Meter (or perhaps
rebuilt)?  Will a new AFM make any difference in the amount of garbage I
spew out the tail pipe?

By the way--I have about 15,000 miles on a rebuilt engine and it runs very
strong and uses almost no oil between changes.

Donald Baxter