Because the PSP version of NFSU2 was rushed, even on real hardware, it has bugs. Here is how to fix them on PPSSPP:

If you are specifically looking to play the original console version of Underground 2 on Android, you typically use a PS2 emulator like rather than PPSSPP. Key Features of NFS: Underground Rivals (PSP/PPSSPP) For those playing the dedicated PSP title via the Rally Relay Mode

: Set to 2x PSP for a balance of speed and clarity. High-end devices (e.g., Snapdragon 865+) can handle 4x or 5x PSP for HD visuals.

Performance depends on your device's hardware, but these settings generally provide a smoother experience: