Broken physics in default car script?

Unity Engine
1

I have to make a car game, and have simply no time to write my own car script, so I decided to use the script from the car tutorial.
Because it has exactly no comments, it’s pretty much impossible to edit.

What’s broken is that the car just stops in mid air sometimes, or does a frontflip.
Here’s a video showing the bugs:
http://wolfos.org/resources/video/ScreenRecordMovie.mov

2

Help would be very much appreciated.

3

Does it help if I say ‘please?’

4

I didn’t made to make this script work with the wheels. They don’ spin at all so I gave up on it.
I suggest spending a few dollars on this system: Edy's Vehicle Physics

5

How does the asset store handle conversion rates? €40 is a little out of my budget at the moment, but I might be able to arrange something…