staypuff

Hi first time poster here, know a little about cars but not much about mercedes. I have a 03 C230 coup, I have searched multiple threads and have not found any with the same symptoms I am having. Problems all started about 4 days after having to replace a rear tire, somone thought it would be fun to throw a handfull of screws down in my gravel lot. Well started having some shutters, started soft but got harder later on. Discovered the trans adapter leak, so I replaced it and went ahead and put a new filter in while at it. At that same time my front passenger wheel speed sensor went out and replaced it. So after all of this work it was running ok but still was shuttering some. Oh and also my gas mileage got pretty bad during all of this, can smell the fumes and now only get 20-22mpg on average. I was getting 28mpg on average. Ok so now poor gas mileage and some shutters that are getting harder. Then here is where I'm getting something unlike anything else I can find. I started loosing almost all throttle after touch the brake pedal. I will have to hit my brakes to slow down a little or come to a complete stop. Then when I hit the gas I have to floor it and it only crawls untill it hits around 3000rpms then it suddenly picks up. But with each shift it slows down and picks up again with the rpms untill I get to like 50mph the its almost like normal. The only difference is if I let off the gas pedal then push back down there is a delay. Also if I put in park or neutral, or any gear for that matter, and apply the brake with my left foot and throttle with my right I get absolutely nothing. No revs at all, normally in park or neutral it will still rev up. I have ran codes and first time it had the acceleration pedal, then second and third time it was throttle possition sensor p0121. Each time I clear it works fine for a bit but comes back fairly soon. Also when it is like that I do not get the shutter anymore except for a really soft hit around 60-70mph almost like a missfire. Thanks for the help I really appreciate it.