Unless you are getting a code for the evap system, your gas cap is fine.

Do the code come up immediately after you reset the code or does it take some time?

When you cold start the engine do you feel the misfire, or do the misfire come on after the SES light?

Do you have a scanner that can view real time data such as short term and long term fuel trim?

Even though you cleaned the MAF, you could have a Bad MAF and no amount of cleaning will get it working right. The app Torque can provide live data of the MAF. Don't bother buying a cheap MAF from eBay or Amazon. Go to a junk yard or buy a used Siemens MAF.

__________________
2006 Infiniti G35
2001 BMW 3.0I E53 X5 Build date 08/2000 SOLD
Lotus Europa 1970 Destroyed by fire
Lotus Europa 1970 S2 Renault Powered
Lotus Type 52 1970 Twincam Webers Powered
PORSCHE 911 Targa 1982 The Garage Queen
Audi Avant donated to Kars for Kids
BMW 525IT Sold
Audi 4000CS Quattro Sold
Jensen Healey Lotus Powered Sold
Opel 1900 Sold
Triumph Spitfire 1971 Sold
Triumph Spitfire 1968 Sold
Plymouth "Cuda" 340 Six pack SOLD