Throttle Body Problem

I bought this car 4 years ago from a friend. The Local Garage (Car Maintenance shop) told me that I need to change the Throttle Body because the idle was not good and I bought one from a friend who was keeping it for replacement. When they installed it, it was doing great but when I start the car in the morning it start up but would not hold the idle so I took the car to the mechanic and he told me that it (the throttle body) has to much carbon deposit and he cleaned it and the car was doing fine except the RPM is always at 11K. So I took it again to the same guy and told him to minimize the idle and he open the throttle black cover and tune it. Since that day, In the morning the car cannot hold the idle and also if I park the car and went for something for about 1 and half hour and starts the car it cannot hold the idle. As a solution, I have to put my foot into the fuel pedal for about 2min to warm up the engine then it (the Throttle body) will hold the idle and warm up the car.

My question is, is there a solution for my problem? Was the mechanic correct to open the black cover of the throttle body to adjust the idle? Can it be tuned back? Please help?