[Blue Bowtie]

I'd suggest removing the air cleaner housing, MAF, and inlet duct/air horn on the throttle body. Using an inspection mirror and light, look into the throttle body for signs of varnish. It's very common to have the throttle plate stick closed in the throttle body bore as you describe due to buildup in the TB, and a simple cleaning with a spray-type carburetor cleaner will do nicely to free up the throttle plate.