Sputtering car

[H2OVapour]

This game has its quirks but this is the wierdest one. I've played through the three first stages of career mode without any issue. Well, except that not a single achievement has triggered but the game itself has been running just fine. Suddenly now I randomly get this problem where My car is slowing down. It's like I'm driving through mud and this usually occurs when I've been burning nitro and run out of it. The car just won't accelerate again until I got new nitro to burn.

Has anyone else had this, is it something I've missed here or is it a bug that all of a sudden has decided to start to haunt Me?