yes now theres your problem, the mechanic adjusting it manually is causing overfueling by the computer, idle rpm of yours is correct and cold start rpm should be around 1500rpm, probably as you said auto choke not working due to computer cancelling out the mechanics settings, yes OBD scanner is the ordinary scanner computer that attaches to the port underneath the dash and you can reset rpms back to factory settings, your problem would be gone, you may also try removing the battery terminals for a while then reconneting them, this often resets it too, its simply seems a electronic issue for now, a scanner would tell better. even average CNG mechanics have a scanner.
