Have a look at the wiring harness under the air box.
I had two severed wires that go to the Crank Position Sensor / Engine Speed Sensor or whatever its proper name is.
I had similar issues, but not quite the same, then it got worse and the car wouldn't start at all. (Plus I got check engine light / no tach / oil light etc)
I'll put money that you have chafed / worn wires in the loom. Have a local guru have a look, if that's the issue, they'll most likely be able to repair it.
Now my car had 280,000km on it, but you could have the issue with so few miles on the car.
- MK4, MK5, MK6 Jetta TDI's in the past
- 2013 Outback 2.5i - wife's commuter
- Subaru Demo
- 02 BMW 330i - weekend fun.