1992 honda civic help?

I just recently purchased a 1992 honda civic cx hatchback with the d15b7 engine..when i start it it idles at about 2500 rpm then gradually decreases when it decreases it starts to violently shake and lose power. I was wondering if a vacuum leak involving the fuel pressure regulator would cause this or if it would be the TPS sensor.. It seems to run a little better when i disconnect the vacuum line running from the throttle body to the fuel pressure regulator but idk as to how to diagnose the problem any help would be much appreciated