Macbook air 2011-mid keyboard keys Q W E R T Y U I O working sporadically
Had the same problem on my MBP13 mid 2012. After 2 months of research and almost spending $600 to replace the top case I found this video:

https://www.youtube.com/watch?v=kh88cn_rtLo

I remove the top case of the key and gave a good clean and they start working again!!!

I know this reply is for an old post but I might help other having the same issue. If this doesn't work, it might be a hardware fault :/