Check Engine Soon light on, Discovery II
 

Prior to light coming on, with smog check coming due, I added CRC Guaranteed To Pass Emissions Test Formula to a full tank of gas (Chevron). Immediately went on 250 mile roundtrip for the day. No problems. Next day, during errands, car hesitated then recovered from stop sign. Following day, starting trip, car stumbled on incline, then 2miles later Check Engine Soon light came on. The next day, local AAMCO testing results: test code P0300 (Random multiple cylinder excess emissions detected). P038 (Cylinder #8 misfire). P036 (#6 misfire). P035 (#5 misfire). P1300 (rapid multiple cylinder misfire detected). P0301 (Cylinder #1 misfire). Shop didn't know what fix would be. Went to leave, vehicle would not start. Towed home, had a beer, was able to start car and reposition in driveway. Looking for diagnostic direction, suspected problem. Mileage 75K.

could be a bad MAF sensor, or the air filter lid is not sealing properly.