Hello everyone. I'm new here and any help is greatly appreciated!

I'm pretty sure im on the right track, but I normally don't work on furnaces so I just want to make sure I'm not overlooking something obvious. I got a call from a friend whose furnace was acting up. When the t-stat calls for heat the inducer motor starts up, pressure switch proves, then the ignitor proceeds to try to light the pilot. It takes several tries for the pilot to stay lit. The pilot itself looks weak but eventually stays lit and the flame prover sends voltage the the main gas valve. The main burners fire up and either go out right away or they will stay on for less than a minute then go out. I suspected a dirty or bad flame sensor so i checked for voltage at the gas valve. The MGV remains energized for 2 to 3 seconds after the burners go out so i eliminated the flame prover as the problem. I think the gas valve is bad, but I want to be for sure before I start replacing parts. Should I check the gas pressure? I also noticed there was a pilot adjusting screw on the MGV . Then again I was thinking the main burners might need cleaned out or something. What do you guys think?