I recently had my 2006 VW Rabbit serviced because I am on a long trip. My car suddenly started faltering, as if I was going over bumps, and the engine light flashed on and off. I pulled over and took a look under the hood. All seems ok. I started up again and the same thing happened. It shudders as it speeds up but not when decelerating. Is this an easy fix, what could it be?