If your engine is non-catalized (20NE as you say), it should have a trim to ajust the %CO at idle.
A wrong trim can cause bad idling.
Anyway you should do the paper clip test and check if there are any error codes saved.
You don't adjust the air flow meter, the meter's job is to give accurate air flow readings to the engine computer to it can adjust the fuel-air mixture. If the air flow meter isn't delivering accurate information to the computer then it needs to be cleaned/repaired, not adjusted. Most allow no type of adjustment anyway. It may be it just needs a clean, how ...