I noticed when you open up the options menu, then go to controls, then to keyboard, the toggle turbo is at the bottom of the list. This makes no sense. It should be right below "turbo" and before "brakes".

I just had to walk some noob through doing it via /alias tlock "+turbo" and /bind "6" tlock . A less then ideal solution I know, but it got the job done for that particular noob. Moving it might make it more obvious as to how to set it.