What you need to know, then a step‑by‑step you can follow. Read it all once before starting.

Why this repair is needed (theory, simply)
- The throttle body is the airflow gate between your air cleaner and the intake manifold. The throttle plate (butterfly) opens and closes to control air going into the engine. Diesel versions of the Toyota L‑series may also have a small throttle/air control valve or idle bypass used for idle control and EGR functions.
- Combustion and crankcase gases deposit oily carbon and soot on the throttle plate, bore and idle passages. Think of it like a door hinge gumming up with grease — the door (throttle) sticks and small amounts of air leak around it unpredictably.
- Effects of a dirty throttle body: rough or high/low/unstable idle, poor throttle response, stalling at idle or when coming to a stop, increased smoke on diesels, sometimes check engine light or limp mode if a sensor is misreading.
- Cleaning restores the smooth motion of the plate and clears the small bypass passages sensors and the ECU use for idle control.

Main components you’ll encounter (what each is and why it matters)
- Air intake hose/duct and air cleaner: carries filtered air to throttle. Must be removed to access throttle.
- Throttle body housing (bore): the metal tube with the throttle plate inside. Carbon collects on its inner surface and on the plate edge.
- Throttle plate (butterfly) and shaft: plate pivots on shaft. If the shaft or bore is gummed, plate may not seal or may stick.
- Throttle position sensor (TPS): electronic sensor mounted on the shaft that tells the ECU plate angle. Don’t soak or damage it — it’s electrical.
- Idle Air Control Valve / Idle Speed Control (IAC/ISCV) or bypass passages: controls a small amount of bypass air to set idle. Often has a pintle or valve and tiny passages that get clogged first. Diesels sometimes use similar idle valves or stepper motors.
- Throttle cable linkage or electronic actuator: mechanical cable or electrical motor. Cable interface must be reinstalled exactly as it was.
- Gaskets and O‑rings: seal throttle to intake manifold. If damaged, you’ll get vacuum leaks.
- Vacuum lines/PCV/EGR connections: often attached nearby. Ensure they’re reconnected and not brittle.
- Sensors nearby (MAF, MAP, IAT): you’ll probably disconnect MAF if present. Keep it clean and don’t spray into it.

Tools & supplies
- Throttle body/carbon cleaner (spray can formulated for throttle bodies). No brake cleaner with power additives that can harm sensors.
- Soft toothbrush, small nylon brush, lint‑free rags, cotton swabs.
- Basic hand tools: screwdrivers, socket set (8, 10, 12 mm typical), pliers, torque wrench if you have one.
- Safety: nitrile gloves, eye protection, shop rags, a catch pan for fluids, clean workspace.
- Optional: small picks (plastic), torque specs from manual, new throttle body gasket if needed.

Safety and precautions (don’t skip)
- Work with engine COLD to avoid burns and to prevent cleaner fumes igniting on a hot manifold.
- Disconnect negative battery terminal if you’ll be unplugging sensors or if recommended for your vehicle; some vehicles require a relearn after battery disconnect (covered below).
- Do not spray throttle cleaner into electrical connectors or the TPS/MAF. Unplug sensors before you spray near them.
- Do not use metal scrapers inside the bore — you can score the surface or damage the shaft.
- Don’t crank the engine with the throttle body removed if the intake is open — it will draw unmetered air or debris into the engine.

Step‑by‑step procedure (typical for Toyota 2L/3L/5L variants that have a throttle/idle valve)
1) Preparation
- Park on level ground, engine off and cool. Engage parking brake.
- Gather tools and cleaner. Put on gloves and eye protection.
- Note routing and position of throttle cable linkage; take photos so reassembly is exact.

2) Access
- Loosen clamp(s) on intake hose and remove air duct between air cleaner and throttle body.
- Remove air cleaner lid and filter if it blocks access.
- If there’s a MAF sensor in the duct, unbolt and set aside (do not spray it).
- Identify TPS and IACV connectors and vacuum lines; label or photograph them.

3) Electrical & vacuum disconnection
- Unplug TPS connector and IAC/idle valve connector (if present). Tape or keep connectors up/out of the way.
- Disconnect vacuum hoses attached to throttle body or nearby ports; mark hoses for reassembly.
- If mechanical throttle cable, unhook cable end from throttle lever (note position) — do not kink or overbend cable.

4) Remove throttle body (optional but preferred for thorough cleaning)
- Loosen and remove the bolts holding throttle body to intake manifold (usually 3–4 bolts).
- Carefully pull throttle body straight off; there will be a gasket — set it aside. Replace gasket if it’s torn or brittle.
- Inspect mating surfaces and manifold opening for debris — cover manifold opening with a clean rag when throttle body is off to prevent anything falling in.

5) Cleaning the throttle body
- With throttle off the car on a bench (recommended), open the throttle plate by rotating shaft to access the back of the plate.
- Spray throttle body cleaner onto a rag and wipe away loose carbon. Use brush and swabs for stubborn deposits. Spray cleaner onto the rag or brush — avoid spraying directly into TPS openings.
- Clean behind the throttle plate edge — a lot of carbon hides there. Work plate open and closed while cleaning but don’t force it. The plate should move smoothly but firmly.
- Clean idle passages and IAC port(s). These are small and can be blocked; use swabs and spray cleaner through the ports until solvent comes out clean.
- Do not use metal tools to scrape bore or plate. Do not spin the TPS or stepper motor.
- Wipe everything dry with a lint‑free cloth. Ensure no cloth fibers remain.

6) Inspect parts
- Check throttle shaft for excessive play or scoring (play indicates worn bushings).
- Inspect TPS connector and IAC for corrosion or damage.
- Inspect and replace gasket if needed. Inspect vacuum hoses for cracks.

7) Reassembly
- Reinstall throttle body with a new or sound gasket. Tighten bolts evenly to factory torque if available; snug is fine for small bolts (don’t overtighten).
- Reconnect throttle cable ensuring there is the same free play as before (or as specified in manual).
- Reconnect vacuum lines and electrical connectors (TPS, IAC). Reinstall air intake duct and MAF if removed. Replace air filter if dirty.
- Reconnect negative battery terminal if you disconnected it.

8) Startup and relearn
- Before starting, check that the throttle plate moves freely by hand without binding.
- Start engine. Idle may be erratic at first. Allow a few minutes for ECU to relearn idle and closed‑throttle positions. For some vehicles you should: with engine warm and A/C off, let it idle for 5–10 minutes, then cycle A/C on/off to help relearn. If you disconnected battery, normal operation may take several key cycles/driving.
- Check for vacuum leaks (hissing, high idle) and that the throttle response is improved.
- If engine runs poorly or check engine light stays on, consult a code reader and the factory manual for throttle position relearn procedure.

What can go wrong (and how to avoid/fix it)
- You damage TPS or MAF by spraying cleaner into electrical parts: avoid spraying connectors; unplug and isolate electronics first.
- You break a vacuum hose or cable: label and handle gently; replace brittle hoses.
- You leave debris in the intake manifold when throttle body off: cover manifold opening while working and clean gasket faces.
- You overtighten bolts and strip threads: snug evenly; use proper torque if known.
- After disconnecting battery, idle may be high/low until ECU relearns — this is normal; follow relearn steps.
- Excessive throttle shaft play or worn bushings: cleaning won’t fix mechanical wear — replace throttle body or have it rebuilt.
- Persistent idle problems after cleaning: could be vacuum leaks, faulty IAC, bad TPS, worn injection pump idle control (on diesels), or EGR stuck; diagnose further.

Quick troubleshooting signs after cleaning
- Idle smooth and stable, no smoke surge — success.
- Still rough or surges — check vacuum hoses, IAC operation, and read any stored ECU codes.
- Throttle sticks — do not force; recheck for bent shaft, damage, or reassembly interference.

Final tips (practical beginner advice)
- Work systematically: take photos before removal and during disassembly so you can put everything back exactly.
- Replace the throttle body gasket every time you remove the throttle body.
- Use only throttle body/carbon cleaner — it’s formulated to dissolve carbon without attacking seals or sensors.
- If you’re unsure whether your 2L/3L/5L has an actual throttle plate (some diesel setups don’t), look for a round plate in the intake bore. If absent, you likely have a different idle control system — still clean any small idle passages and IACs you find, but do not attempt to remove things you can’t identify.

Do this carefully and you’ll fix most idle and response problems caused by carbon buildup.
rteeqp73

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