The Toyota 3S-FE engine control unit (ECU) pinout varies slightly by vehicle model and production year, particularly between early 1990s models (like the Celica and Camry) and late 1990s models (like the RAV4). Common 3S-FE ECU Pinout Documents (PDF)
Probe the PIM pin. Voltage should sweep smoothly from ~1.5V at idle to ~3.5V+ at Wide Open Throttle (WOT). A "stuck" voltage here will cause the ECU to default to a rich/lean limp mode. 3s-fe ecu pinout pdf
Because Toyota changed wiring diagrams frequently, there isn't just "one" PDF. Here are the best resources to find the correct diagram for your specific chassis code (e.g., ST184, SV21, etc.). The Toyota 3S-FE engine control unit (ECU) pinout
If you cannot find a PDF, or you suspect your harness has been modified, you can reverse-engineer the pinout yourself. This is tedious but foolproof. Voltage should sweep smoothly from ~1