I have a VW Jetta 1.4tsi 122 (2008) and it has a strange behavior.
First of all, a have noticed that it doesn’t keep the same rpm when runs on idle. For example, when I stop at the first traffic light it runs at 600rpm and at the next traffic light it runs at 1000rpm.
Also in the morning when its cold it keeps 600rpm and when the temperature rises to 90deg it climbs to 1000rpm. Before five months when I started it in the morning it was stuck at 3000rpm (nothing was pressing the acceleration pedal) and when I restarted it, it was ok.
Finally yesterday night I couldn’t start it. The starter was working correctly and the car seemed to have “started” but it was running at 200-300rpm and eventually turned off. I replaced the battery with a new one but it did the same thing.
Finally, I started it by pressing the gas pedal and after the engine started the fumes seemed to contained unburned fuel. The same happened before six months but my mechanic insists that the car is ok because there are no error codes.
What could cause the problem? Every time that I had the problems I was refueling from different fuel station so I don’t think that it is a fuel problem.
Edit: about the fume I am not 100% that was containing unburnt fuel. It had a light color but I am not sure about it.