Rockstar did not include a spawn cheat for the Caddy (golf cart) in GTA IV.
Dial on Niko's phone:
486-555-0100 – Health/Armor486-555-0150 – Weapons 1486-555-0100 – Weapons 2227-555-0142 – Super GT (Comet)227-555-0175 – Sanchez227-555-0168 – NRG 900227-555-0147 – Jetmax (boat)227-555-0198 – Annihilator (heli)Using cheats disables achievements/trophies on that save.