Rockstar Games never ported GTA 4 to the PSP. The PSP simply lacks the hardware power (RAM and CPU) to run the GTA 4 RAGE engine. Fan-Made "Mods":
: Files disguised as ISOs that are actually executable viruses. gta4pspdownloadiso fixed
: The HUD, health bars, and weapon wheels are redesigned to match the aesthetic of the HD-era GTA games. Rockstar Games never ported GTA 4 to the PSP
Be extremely cautious of any site asking you to complete a "Human Verification" survey to unlock the download. No legitimate PSP ISO requires a survey to download. These sites prey on fans looking for a game that doesn't exist. : The HUD, health bars, and weapon wheels
If you are looking for a "fixed" version of such an ISO, here is a report on the current state of these files and how to actually get the best experience: 1. The Reality of GTA 4 on PSP No Official Release: