I have a 1987 Chevrolet Silverado Pickup.It has a 5.7 ,Throttle body injection. The problem is It occasionally stumbles and has a rough idle. Recently the check engine light came on, showing a code 22 and a code 42.

check the map sensor vacuum hose first.

more than likely a vacuum leak get a can of carb cleaner and spray around intake gaskets throttle body vacuum hoses if idle rises or stumbles you have leak in that place

You may just have to service your yhrottle body and run a fuel injection service... also inspect your idle control motor.

Try cleaning TAC valve, spray throttle body cleaner in upper right of opening clean well.

Firing order for the 4.3 Throttle Body Injected motor which is likely what you have 1-6-5-4-3-2 ------- Distributor rotates clockwise

If your getting a check engine light on the dash,you need to correct the problem first,If you want to clear codes from the computer,you will need to unhook the battery for about 1min.
But there is no resetting of the computer.If your truck is idling rough and dying,you still have a problem somewhere,You should be looking for any vacume leaks,or one of the sensors on the throttle body like the IAC,idle air control,

Try replacing your spark-plugs/wires, cap/rotor, air-filter. Spray some WD-40 on the throttle-body recoil spring.Get a can of carburettor/throttle-body cleaner and spray the inside of the throttle-body.

sounds like your egr valve is gummed up or bad. this is located behind the throttle body and has a single vaccum tube connected to it. if the diafram is still good you can remove it and clean it with WD 40 until the plunger works smooth

throttle gasket leaking or vacuum leak of some sort