On cold mornings (freezing and colder) my 2013 Beetle TDI occasionally turns over like it has a dead battery; cranks very slowly and stops cranking before it can start or won't turn over at all. I replaced the battery last season but it didn't cure the problem. Took it to a VW specialist (non-dealer) and he couldn't find anything wrong. No codes display. On some days it will start fine, idle normally, but when I start moving the engine bogs like it's firing on a couple of cylinders. It sometimes dies before I can start moving, sometimes keeps running poorly until it warms up and runs right. The VW specialist said it may be moisture (condensation?) in the intercooler causing the problem when it freezes and suggested I don't baby it. Driving it harder doesn't seem to make a difference. It also has an issue when driving with just enough throttle to maintain speed on level road, like a cylinder cuts out then in again over and over. Throttling back or more throttle and it disappears. This can happen summer or winter. Not sure if it's related but I can live with that. Any ideas on what could be causing the first problem?