Misfiring but no CEL
You could be lean, due to a small vacuum leak. The additive you tried would actually enrichen the mixture and reduce the miss. Try spraying brake-clean on the intake gasket areas, around the egr valve, or any other vacuum operated device. If the miss stops while the spray is present, you found the leak. Also, the way you should "clean" a MAF is by removing the sensor from it's housing and spraying brake-clean on the two sensor wires. Do not scrape the sensors, be carefull not to break the wires. Just spray until clean. Then reinstall.Good Luck.