I had an issue like this a few weeks ago. When I reconnected the black wifi cable I slightly disformed the silver round receptacle on the logic board. I used a pair of small needle nose pliers to repair it. I also thoroughly cleaned the antenna wire and receptacle (99.9% alcohol and a softw cloth wipe)... (They can be a pain to get reconnected sometimes, you know, twist, snap, twist).
Another problem, if you can't resolve it with all of the above great advice from others, is a potentially flaky wifi antenna chip. Their could be a stress break in a solder joint and by applying and removing pressure creating a temporary connection.
I had an issue like this a few weeks ago. When I reconnected the black wifi cable I slightly disformed the silver round receptacle on the logic board. I used a pair of small needle nose pliers to repair it. I also thoroughly cleaned the antenna wire and receptacle (99.9% alcohol and a softw cloth wipe)... (They can be a pain to get reconnected sometimes, you know, twist, snap, twist).
Another problem, if you can't resolve it with all of the above great advice from others, is a potentially flaky wifi antenna chip. Their could be a stress break in a solder joint and by applying and removing pressure creating a temporary connection.
http://www.parts4repair.com/iphpne-4s-wifi-antenna-chip/
good luck!