RE: wheels keep turning at idle
Anthoop has it, it's a tuning issue. Lean the LSN while simultaneously turning down the idle until it will stay running without throttle or clutch engagement. If that really isn't it, get slightly stronger clutch springs.
For the benefit of anyone else reading this thread and wondering why the wheels move when the car is OFF the ground; this is completely normal. However, when placed on the ground the car should stand still and idle without dying.