Ive recently been experiencing a few problems with my 2006 Audi a3 2.0 TDI. Sometimes when trying to start cranking takes a while, sometimes not even starting. I got told by a friend it could be my heater plugs which I then got replaced,but still the problem continued, so i took it to a garage who checked the battery which he said was fine and changed my fuel filter, Mechanic told me using supermarket fuels has to much crap in as they dont clean out there tanks properly,my car ran fine for a few weeks but lately its been playing up again when starting, any ideas what this could be? No problems are coming up on diagnostics tools. Another problem im experiencing is a shuddering sometimes at speed, on one side of the car?

Thanks for any feedback, Kev