Just a bit of background to this one.
As my car is still in warranty I decided to try out the dealers for a 2 year service.
When Ive got the car back, tickover is lumpy and the engine is definitely not running as smoothly as it was.
Potentially relevant bits they touched (apart from "visual inspections" ) that are connected to the oily bits/ecu & sensors are "filter engine" (whats that???) "filter fuel" and "check dtc with diagnostic tool"
Any ideas what they could hgave stuffed up with

??