Does it run well at higher rpms? Could be something simple like loose mounting bolts causing a vacuum leak. Do you smell raw gas? Check the mounting bolts/screws for the fuel pump as it usually relies on vacuum created by the motor to suck gas from the gas tank. Look at the fuel line for loose connections, cracks, etc. I actually cured a bad idle when I found a kink in the fuel line!
Try the cheap fixes first.
Good luck.