ALL GDI engines will eventually foul their intake valves. Especially if the engine is turbo-charged.
The fouling occurs when blow-by is recycled into the intake air-stream via the PCV system. The oil vapors and condensate from the crank impinge on the intake manifold side of the valve and valve stem. When the engine is heat-soaked at operating temperature, the oil vapor and condensate hit the now HOT valve and valve-stem, and bake onto the surface. At the miles increase, the carbon build-up can get pretty extreme. Hard starting, rough idle, poor air-flow, restricted air-flow, pre-ignition - lousy mileage, rotten performance - the list goes on.
To prevent this, install a catch-can between the PCV valve and the intake. There is a whole spectrum of available catch-cans out there. I bought one on Amazon.ca for my wife's 2020 Titanium with the 2.0 liter 4 cylinder. It was installed at 16,000 km (10,000 miles), and I'm surprised at how much the catch-can system actually collects. It's that much less that gets thrown on the hot intake valves.
Is it a 100% solution? I don't know yet. The Chinese knock-off design I bought for $25 (and installed in the 2020 Escape) is an accurate copy of the Mishimoto system of baffles, which costs US$150. I know that's kind of shitty to do, but I couldn't afford the Mishimoto units - which are built in China anyway, sooo....
All I DO know, is that the intake valves on my 2012 F-150 with the 3.5 liter ecoboost are fouled. I put on two catch cans at about 180,000 km, so about 40,000 km ago. Did it prevent further build-up? I hope so. I need to remove the carbon buildup with a crushed walnut-shell blasting, but that's for Spring 2022.
I'm going to replace the two Princess Auto air-dryer / "catch-cans" on my F150 with the same unit I used for the Escape.