I have the exact same issue.
The issue is due some type of issues between the Wireless card and the Bluetooth, possibly associated with OSX Mavericks.
I've run through all the recommended solutions, including changes to my router settings etc. I've tried it with several routers, but to no avail.
- If I startup or wake my 2013 Retina MBP with Bluetooth enabled, it can take anywhere from 10-30 seconds to connect to wifi. Sometimes it it will not connect at all. When Bluetooth is disabled, wifi will connect in less than a second.
- While using speedtest.net I could signicantly effect my wireless connection speed simply by turning Bluetooth on and off. In some cases my internet connection would slow down by as much as 50% by turning on Bluetooth.
- I previously owned a 2010 iMac, which had none of these issues.
I've spoken to Applecare and they have assured me that a firmware fix is coming. That was several months ago.
Apple has
- Not publically acknowledged this issue, which is clearly very widespread.
- Applecare has been privately telling customers that a firmware fix is coming for almost a year.
- This issue has not been addressed in either of the last two Mavericks updates
This leads me to believe that the issue is strictly hareware related and Apple is doing what they can to avoid a costly recall. If they can delay their customers long enough, then they will be responsible for any covering the cost of any fix.