Since upgrading to OS X Lion, I’ve had all manner of Wi-Fi problems, including dropped connections, very high ping times and generally erratic performance combined with very little stability and connection uptime. The problems are well documented around the web, including on Apple’s own support forums. There’s no official fix yet, and all of the recent AirPort updates in developer seeds of OS X Lion haven’t really changed the status quo. The problems happen on a number of Macs, including the late 2009 model iMac I have (iMac11,1 in Apple nomenclature) which features an Atheros Wi-Fi chip.
The problems only happen with certain Wi-Fi access points, and connecting to Apple’s own Airport Extreme is reportedly fine. While it’s a really nice access point, it’s a lot of money to mitigate what’s resolutely a software problem which Apple will eventually fix. I did eventually go out and get a cheap 802.11n combined access point and modem router, and while performance came back and stability was mostly there, it did start causing kernel panics in the Atheros kernel driver; that’s something that didn’t happen before when connecting to my old 802.11g access point.
Since the problem wasn’t there in Snow Leopard, I’ve been experimenting for the last day with the old Snow Leopard driver for the Atheros hardware (v3.2, compared to v4.0 that shipped with Lion), and everything seems to be back to normal. I’ve had a stable, performant connection with no kernel panics, and while it’s only been a day without problems (on both new 802.11n hardware and older 802.11g) that’s good enough to say that I think it’s fixed, given the horrible quality of the link before on the v4.0 driver.
It’s trivial to downgrade to the v3.2 driver (shipped as a kernel extension or kext) using a kext utility developed for people bringing up OS X on non Apple hardware and the Snow Leopard kext harvested from an old Time Machine backup.
I’ve packaged both together and uploaded them to my Dropbox. Unzip, then unzip the Kext Utility, then drop the kext on the Utility app. Supply your password, reboot and then hopefully all is well with your Wi-Fi connection. Obviously only have a go if your Mac has Atheros Wi-Fi hardware!
Update (13th May 2012): I’ve finally written about backing up and restoring your current Wi-Fi kext!