Hi Liam,

You really should bring the car back to the garage that did the work. In many modern diesel engines the injectors and ECU computer need to be electronically 'matched' and that may not have been done in your car's case. Also, this generation of the E-Class is known to have common wiring loom problems, with oil leaking into the ECU causing a lot of expensive damage. It's worth checking that hasn't happened.