SOLVED: 4.6is with "throttle briefly jammed"

[Estoril]

Hi guys. Three times now when starting the car after it had cooled down (about 2-3 hours of being parked), the car would crank but the RPMs would quickly drop back to 0. Starting it up again and the RPMs would fluctuate for a few minutes before going back to a steady RPM.

I went by the mechanic to have it checked, who got the "throttle briefly jammed" error code. He adviced me to take off the throttle body and clean it off with brake cleaner and a soft brush. On the forum I read a lot about the throttle position sensor. Any advice on what would be the best next step, before I start cleaning the throttle body?

P.S. I also read somewhere that a rip in the intake rubber would also cause this. The mechanic checked for vacuum leaks but didn't find any