broken line.. where to find?

i just bought a 92 mustang lx hatchback w/ the v-8 w/ some mods. after i took off the stock h-pipe and switched it w/ an offroad h-pipe and by-passed the smog pump.. i noticed there was a line broke.. it's on the passanger side near the firewall. it's white and connects up near the throttle body and the other end is in a square connector w/ 4 or 5 other wires. all have round ends connecting.. i'm not sure if it's a vaccuum line or O2 sensor.. also it doesn't seem to run quite rightand doesn't have the power it should.. has a slight low pitched popping sound.. the check engine light comes on once i get into the higher rpm's... it's possible that i may have fouled a plug or something. i'm going to replace the plugs and wires here soon.. does anyone know what this line is and what it does????