I own a 2014 Ford Focus, with a 4-cylinder turbocharged engine. A few years ago, it developed a rather interesting issue. After I put gas in the tank, it gets hard to start, and is hard to keep running for the next few minutes.
It's not the amount of gas in the tank that triggers this, it's the amount I put in while fueling. If I put in half a tank, the symptoms are exactly the same, regardless of if this fills the tank from almost empty to half, from 1/4 to 3/4, or from half to full. If I put in a quarter-tank's worth of gas, the symptoms aren't quite as bad, and if I fill it all the way up, it usually takes at least two tries to get it started and I have to keep a slight bit of pressure on the accelerator for a few minutes to keep it from stalling.
I don't have any idea how to go about diagnosing something like this, so I haven't tried anything beyond testing with different grades and brands of gas (no change). Aside from a slight cooling system leak, there's nothing else wrong with the car.
Anyone got any idea what the problem could be?