1994 Plymouth Acclaim Extremely rough idle, won't rev

I'm working on my brother's Acclaim that recently started running very poorly. At idle, the engine shakes violently and nearly stalls. If you try to rev the engine, it runs even poorer and with the air filter and housing removed raw fuel drops are visible coming up from the throttle body. There is a noticable fuel smell. The check engine light is on and it is reporting a 13, MAP vacuum error. There are no apparent vacuum leaks. I replaced the MAP sensor with no success. Oddly enough, if I introduce a vacuum leak into the system by removing the hose going to the brake booster the engine runs much better. This tells me that there is not enough air going through the throttle body to burn all the fuel. Am I looking at rebuilding the throttle body or is there another potential issue? I don't want to spend a lot of money on the car since it will probably be replaced by the end of the year, but I need to get it running until then.

Thanks in advance.