99 chevy venter need help!!!!!

hello my 99 chevy venture is running really rich doe anyone know why

Depends on how you know it's running rich? (A/F meter or emissions failure).

Start by checking the O2 sensors. On my Vette the O2's started to go bad but were not setting codes (within range). Luckily I had a A/F meter hooked up and could tell it was time to replace.