There is a idle adjustment and a high speed adjustment and a four or five gas analizer should be used.Does'nt have to but should. We don't touch these during regular maintenance unless a problem is noted by the customer or on a test drive. These adjusters are VERY touchy and it take a fair amount of time to get them just right. If the car is running ok and the plugs look good ,I'd leave it. My two cents worth. Brian