1978 450SE fuel injection V8 problem
 

I have this mercedes that has been sitting for years. I Cleaned out the entire fuel system and run it every other day to clean it out further. When it runs it runs Great. My question is, everytime I go to start it, I have to pour a little gas in the throttle body. It will run good until it warms up. Then as I am watching it, the throttle valve falls(opens) a little bit and the car dies. Then (sometimes) I have to put a little more gas in the Throttle body to start again. not a mechanic. hope this makes sence. thanks.