I started to develop a problem with my Passat when after about 15 minutes of the car running it started to lose power momentarily and the EPC light would come on. Eventually this was accompanied by the catalytic converter warning lamp.
Car would then stall when you came to a standstill and would be hard to start again, but would eventually get going. This just went on every day for the weeks I should have got it fixed.
I took it to the Volkswagen dealer and they were talking about trying lots of things including a compression test and wanted over £300. All without a guarantee of actually fixing the problem! I got the impression that they didn’t know what the problem was.
My Vagcom diagnosed it as a problem with engine speed sensor – also believed to be known as the crank sensor. I got a local, trusted mechanic to change it for £70 and it’s been fine since.