mid-2011 MBA: sluggish wifi on WPA/WPA2 networks Machine specs: Mid-2011 MacBook Air with a 1.8 GHz Intel Core i7 processor, and 4 GB DDR ram, Intel HD Graphics 3000 384 MB, OS 10.9.2 (Mavericks).

Wifi connection is sluggish with multiple ISPs on various WPA/WPA2 networks (home, friend, family, etc.)  but works fine on large public networks (e.g. Starbucks) as well as the university network where I am a student. My other apple devices (iPhone and iPad mini) work fine on the same WPA networks which are giving my 2011 MBA trouble. 

After and in-depth search of this site and a few others, I’ve tried the following trouble-shooting steps to no avail:


Hardware inspection of airport card by Apple technician revealed no damage
Fresh “erase and install” of the OS 10.9.2 (did not use time machine backup out of fear of cloning the problem back onto my machine)
verified and repaired permissions and disk from Disk Utility
verified and repaired Keychain 
verified that the wifi was also sluggish in safe mode and restore mode
hard reset of WIFI by erasing the appropriate system preferences plists
created a “test” location in Apple network preferences; erased and created Wi-Fi in network preferences
flashed the PRAM/ NVRAM
changed DNS servers manually 
checked the activity monitor and ran Sophos Anti-Virus to check for malware, viruses, etc. 
turning off the bluetooth
dragging the appropriate network to the top of the list
renewed the DHCP lease from network preferences
reset the MTU manually to 1453 (default is 1500)
flushed the DNS cache in Terminal (dscacheutil -flushcache)
turned the Apple security firewall on and off again


At this point I'm thinking it actually may be a hardware problem that was overlooked by the Applecare technician.  Would it be worth buying a new airport card and installing it myself?

Thanks, all, for the help!
Turns out one of the internal antennae in the monitor was not properly connected to the airport card.  After properly securing the antennae the wifi problem was fixed immediately.  Evidently the problem affected the signal strength and reliability, even though it showed full bars on the menu bar.