1) Goal and symptoms (theory)
- What build-up does: PCV/oil vapor, unburned fuel and soot, and EGR gases deposit oily carbon inside the intake plenum, runners, throttle bore and EGR passages.
- How it causes faults: deposits restrict and make airflow inconsistent, foul throttle plate movement and idle control, alter MAF/TP/MAF-equivalent readings, and change local fuel/air distribution. Result: rough idle, surge, poor throttle response, reduced power, misfires, higher emissions or check-engine lights.
- What cleaning fixes: restores smooth, predictable airflow and moving parts, removes vacuum/flow restrictions and sensor-contaminating deposits, and (when gaskets are renewed) eliminates intake vacuum leaks — letting the ECU return to correct fueling and idle control.

2) Preparation and diagnosis (theory + purpose)
- Verify symptoms and scan for codes (MAF, MAP, EGR, fuel trim, intake leak) so cleaning is justified. Long-term high short-term fuel trims or EGR/PCV codes point to deposits.
- Safety & containment: relieve fuel pressure, disconnect battery (prevents accidental cranking and protects electronics), work in a ventilated area. Relieve pressure because you’ll disconnect fuel lines; disconnect battery to protect sensors/actuators and avoid sparks around fuel.

3) Access: remove intake tract and components in order (theory)
- Remove airbox and intake ducting so you can reach the throttle body and intake plenum. Purpose: access and avoid contaminating MAF/air sensor.
- Label and disconnect vacuum lines, electrical connectors, PCV hose, and any EGR or secondary air plumbing attached to the intake. Purpose: prevent mis-reconnections and protect sensors.
- Remove throttle body (unbolt) and set aside; cover throttle body opening to prevent debris entry. Theory: the throttle bore is a major deposit site that affects idle control, and removing it lets you clean the bore and throttle plate thoroughly without damaging sensors.

4) Intake manifold/plenum removal (if required) (theory)
- Unbolt and remove the upper intake/plenum to expose runners, injector rails (careful with fuel rail if needed), and EGR passages. On many 4Runners you’ll remove bolts in a cross/sequence to avoid warping — this is to protect mating surfaces.
- If fuel rail removal is necessary, relieve fuel pressure first and cap lines. Purpose: allows full access to runners and valve areas; some deposits are inside runners and behind throttle body.

5) Inspection (theory)
- Inspect mating o-rings, gaskets, PCV/oil separator, vacuum hoses, intake manifold for cracks or warpage. Dirty PCV or failed oil separator is a major source of oily deposits. Replacing these prevents recurrence.
- Check valve stems and intake port deposit severity. For heavy valve carbon (common on DI engines), chemical spray alone may not work — mechanical or walnut-blast is required.

6) Cleaning methods and why each is used (theory + practical)
- Throttle bore & plate: use throttle-body/intake cleaner and a non-abrasive brush or cloth. Remove varnish and sticky oil. Why: throttle sticking and mispositioning changes idle control and TPS readings.
- Intake plenum & runners: wipe or brush out loose deposits; then use an appropriate intake cleaner or soak removable parts. Purpose: removes flow restriction and restores symmetrical airflow between cylinders.
- EGR/cooling passages & PCV: remove and clean passages and oil separator. Why: EGR ports and PCV contribute direct soot/oil into the intake; cleaning prevents continuous recontamination.
- Valve/port carbon (if port-injected vs DI differences):
- On port-injected engines (most 4Runners), fuel washes valves somewhat so deposits are lighter; cleaners and brushes often suffice.
- On direct-injected or heavily sooted engines, walnut blasting or specialized media is often required to remove heavy carbon without damaging valve/seat surfaces. Why: chemical cleaners can’t always remove hard carbon; mechanical media restores airflow and valve sealing.
- Avoid spraying MAF or sensors; protect electrical connectors and openings with clean rags to prevent debris ingress.

7) Reassembly and seal restoration (theory)
- Replace intake manifold gaskets, throttle-body gasket, and any O-rings or PCV components you removed. Theory: old gaskets often leak; cleaning plus new seals restores manifold vacuum integrity, which is essential for correct fuel trims and idle.
- Torque bolts in the recommended sequence to spec (prevents warping and uneven sealing).
- Reconnect vacuum lines, sensors, fuel rail, and electrical connectors exactly as labeled.

8) System priming, checks, and start-up (theory)
- Reconnect battery. Prime the fuel system (key-on cycles) if fuel was disconnected, to avoid lean cranking or injector issues.
- Start engine and allow to idle until warm. Theory: ECU will re-calibrate idle and adapt fuel trims; a stable idle indicates flow/sensor readings have returned to normal.
- Check for vacuum/fuel leaks and listen for irregularities. Scan for codes; clear stored codes and verify trims and sensor outputs return to normal within a short drive cycle.

9) Verification and follow-up (theory)
- Short road test with light and heavy throttle to confirm throttle response, absence of misfire or surge, and improved drivability.
- Re-scan for codes and review fuel trims: long-term fuel trims should move toward zero if the problem was intake restriction/contamination.
- Replace PCV/oil separator if not already done and consider periodic inspection to delay recurrence.

10) Limitations and when further repair is needed (theory)
- If cleaning doesn’t resolve symptoms, the fault might be: failing fuel injectors, clogged catalytic converter, ignition faults, intake manifold warp/crack, or valve-seat/cylinder issues. Carbon cleaning removes airflow/fuel distribution problems but won’t fix mechanical failures.
- For heavy valve carbon on DI engines, walnut blasting by a shop or valve machining may be necessary. For persistent vacuum leaks, intake manifold replacement or gasket surface repair may be necessary.

How the repair fixes the fault — summary
- Removes physical restrictions and sticky deposits that alter airflow and throttle movement.
- Cleans EGR and PCV paths so oil/soot recirculation stops accelerating re-contamination.
- Restores accurate sensor signals (throttle position, idle air control behavior, MAF/MAP readings) so the ECU can return fueling and timing to factory targets.
- Replacing seals eliminates vacuum leaks that cause unmetered air and skew fuel trims.
Net result: stable idle, correct fuel trims, improved throttle response and power, reduced emissions and fewer codes related to intake/EGR/PCV.

Safety and cautions (short)
- Don’t inhale cleaners; use gloves/eye protection. Avoid open flames — solvents and fuel are flammable. Don’t spray MAF or electrical connectors. Replace gaskets and O-rings — reusing brittle seals causes new leaks. When in doubt for heavy valve carbon, use a specialized shop.

That’s the ordered procedure with the underlying theory and how each action corrects the fault.
rteeqp73

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