- Safety first
- Wear safety glasses and gloves; keep loose clothing/hair away from the throttle linkage and running engine.
- Work in a well-ventilated area; engine bay parts get hot. If you must test with the engine running, be extremely careful of moving parts (belt, throttle plate).
- If you disconnect electrical connectors, do not short battery terminals; if you remove the battery negative, re-learn/clear codes per service manual if needed.

- What the TPS (Throttle Position Sensor) does — short, for context
- The TPS senses throttle plate position and provides a signal voltage to the engine computer (ECU) so the ECU can manage idle, fuel, advance and transmission logic.
- Typical TPS has three wires: 5 V reference, signal, and ground.

- Tools required (detailed description and how to use each)
- Digital multimeter (DMM)
- Description: Measures DC voltage, continuity, resistance. Should be able to read 0–20 V DC accurately.
- How to use: Set to DC volts (20 V range). Black lead to good ground (battery negative or chassis), red lead to the wire/pin being tested. Read stable voltage; avoid contact with moving parts.
- Why required: To verify 5 V reference, signal voltage, and to check for smooth change as throttle moves.
- Small backprobe pins or thin insulated paperclip
- Description: Used to access connector terminals without disconnecting the connector.
- How to use: Insert gently between harness connector and female terminal to contact the pin while keeping connector attached.
- Why required: Allows testing live signals without breaking connector wiring or introducing errors.
- Basic hand tool set (ratchet, sockets 8/10/12 mm, small extension, screwdriver set)
- Description: Standard sockets and screwdrivers to remove engine covers, air intake hose, or TPS mounting screws.
- How to use: Use correct socket size to avoid rounding fasteners; work calmly to avoid stripping.
- Why required: To access the throttle body and remove/replace the TPS if necessary.
- Needle-nose pliers and flat-blade screwdriver (small)
- Description: For removing clips, hose clamps, or gently levering connectors.
- How to use: Pliers hold or pull connectors; screwdriver gently pries tabs.
- Why required: Many connectors have locking tabs; these tools help without damaging clips.
- OBD-II scanner with live data (recommended)
- Description: A basic code reader can show stored codes; a scanner that reads live PIDs can display TPS percentage or voltage in real time.
- How to use: Plug into OBD port, read codes, then view live TPS data while slowly opening throttle.
- Why required: Confirms ECU sees TPS changes and isolates mechanical/electrical problems from ECU or harness issues.
- Throttle body cleaner and shop rags (optional but recommended)
- Description: Spray cleaner formulated for throttle bodies; rags to clean.
- How to use: Remove intake boot, spray and wipe carbon around throttle plate (engine off). Avoid spraying electrical connectors.
- Why required: Dirty throttle plates can cause odd TPS readings or binding; cleaning can fix symptoms without replacing sensor.
- Replacement TPS or throttle body (explain which might be needed)
- Description: TPS alone (3-pin sensor) or a throttle body assembly with integrated sensor (some model years).
- How to use: Replace component per vehicle procedure (disconnect battery, remove connector and screws, fit new part, torque to spec, reconnect).
- Why required: If TPS is dead/discontinuous or drifted out of spec; some newer units are integrated and require replacing the whole throttle body.
- Electrical contact cleaner and dielectric grease (optional)
- Description: Cleaner for connectors; grease prevents corrosion.
- How to use: Spray/clean connectors, let dry, apply small amount of dielectric grease to plug seals.
- Why required: Fixes poor contacts that can cause intermittent TPS signals.
- Torque wrench (optional, recommended for reassembly)
- Description: Ensures screws/bolts tightened to manufacturer specs.
- How to use: Set to spec, tighten bolts in sequence.
- Why required: Prevents overtightening or leaks (if throttle body removed).

- Preparatory steps (safe setup)
- Park on level ground, engine off and cool (unless instructed to test with engine running); engage parking brake.
- Remove engine cover or intake snorkel if needed to access throttle body and TPS connector.
- Identify TPS location: on the throttle body, attached to throttle shaft/plate; usually a small rectangular 3-pin connector and 2–3 mounting screws.

- How to test the TPS (engine off — static checks)
- Check connector and wiring visually for damage, corrosion, or loose wires; clean if dirty.
- Find the pinout: look up a wiring diagram for your 4Runner year or use backprobe to find which pin is 5 V reference (should read ~5 V with ignition ON), which is signal, and which is ground.
- With ignition ON (engine off), use DMM:
- Black lead to battery negative or chassis ground.
- Red lead to the reference pin — you should see ~5.0 V (2.5–5.0 V sometimes in older models; check manual if available).
- Red lead to ground pin — should read ~0 V.
- Red lead to signal pin — with throttle closed you should see a low voltage (commonly ~0.3–1.0 V). Slowly open the throttle by hand (or have an assistant press pedal) and watch the signal voltage rise smoothly and steadily up to around 4.5 V at wide open (exact numbers vary by model; smooth, linear change is the key).
- Resistance test (with ignition OFF, engine cool):
- Remove TPS connector and measure resistance across appropriate terminals while gently rotating the throttle shaft by hand (use screwdriver in throttle shaft slot or move linkage). Resistance should change smoothly without big jumps or dead spots.
- If there are sudden jumps or dead spots, TPS is likely failing.

- How to test the TPS (engine running — dynamic check; be careful)
- Only attempt if comfortable and safe to do so (keep fingers clear of throttle plate).
- With DMM connected to signal and ground (backprobed), start engine and observe voltage at idle; it should be stable and low (often <1 V). Slowly press accelerator and observe smooth voltage rise without spikes or drops. Erratic changes indicate a bad TPS or wiring issue.
- Use OBD-II scanner live data to monitor TPS % while varying throttle — it should increase smoothly and match pedal movement.

- Interpreting test results (what’s normal vs bad)
- Good TPS
- 5 V reference present, ground is 0 V.
- Signal voltage rises smoothly and steadily with throttle opening (no jumps, spikes, or sudden drops).
- Resistance changes smoothly when rotating shaft.
- Bad TPS or wiring
- No 5 V reference — wiring or ECU problem (check harness, fuses).
- Signal voltage stuck at one value or jumps erratically — sensor is probably bad or wiring intermittent.
- Dead spots or sudden jumps in resistance tests — replace TPS.
- Codes like P0120–P0124 (TPS circuit range/Performance) typically point to TPS issues — confirm with measurements.

- Replacement: when required and what to replace
- Replace TPS when tests show:
- No smooth change in signal voltage with throttle movement.
- Intermittent signal or large voltage spikes.
- Resistance test shows dead spots.
- Confirmed diagnostic trouble codes plus failed voltage checks.
- Which part to get
- Older 4Runners (mechanical throttle bodies) usually have a removable 3-pin TPS sensor; you can buy the specific TPS for your engine/year (OEM or quality aftermarket).
- Newer 4Runners with electronic throttle bodies may have the TPS integrated into the throttle body assembly; replacement requires entire throttle body.
- Get the exact part by VIN/year/model. Commonly listed as “Throttle Position Sensor (TPS)” or “Throttle Body Assembly (with sensor)”.
- Replacement notes
- If replacing just the TPS: remove connector, remove screws, swap sensor, torque screws to spec, plug in connector.
- If replacing throttle body assembly: follow factory procedure (often involves disconnecting intake, coolant hoses, electrical connectors, then re-learning throttle/idle per service manual).
- After replacement, clear codes and test; some vehicles require idle relearn or ECU reset.

- Extra troubleshooting tips
- If you get no 5 V reference, check ECU fuses and wiring back to the ECU before replacing the TPS.
- Check connectors for corrosion; clean and use dielectric grease.
- If throttle body is sticky, cleaning can restore proper TPS readings; only use throttle body cleaner and avoid spraying into connectors.
- If codes persist after new TPS, inspect wiring harness for chafing, broken wires, or intermittent connector contacts.

- Summary quick-check (what you should verify)
- 5 V reference present with ignition ON.
- Ground present.
- Signal voltage changes smoothly from low (~0.3–1 V) at closed to high (~4.5 V) at WOT.
- No intermittent jumps or dead spots; if present, replace TPS (or throttle body if integrated).

- Final safety/reminders
- Don’t force or jam connectors; avoid touching the throttle plate while engine runs.
- If unsure at any point, consider a professional mechanic — replacing sensors improperly or incorrect wiring work can damage ECU or create driveability issues.


rteeqp73

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