Purpose and symptoms (short)
- Why clean: oil/PCV vapors, EGR soot and general fuel/oil residues deposit carbon and varnish inside the intake plenum, runners, throttle body and EGR/PCV passages. This reduces effective cross‑section, disturbs airflow distribution, fouls idle control and throttle position, and impairs metering (MAP/MAF, IAC/idle).
- Symptoms: rough or hunting idle, stalling, poor throttle response, reduced power/efficiency, surging, check‑engine codes for lean/idle control or misfires, sticky throttle.

Ordered procedure with theory at each step
1) Preparation and safety
- Disconnect battery negative. Relieve fuel pressure only if you will remove fuel rails (usually not needed for plenum removal). Work in a well‑ventilated area, wear gloves/eye protection.
Theory: Prevents accidental cranking while electrical connectors are off and reduces fire risk with cleaning solvents.

2) Remove intake ancillary components (air box, intake hose, MAF/AFM if applicable, vacuum hoses, electrical connectors)
- Label hoses/connectors and take photos. Remove the throttle body from the intake plenum if you will clean it separately.
Theory: You must access the plenum/runners and throttle body. Removing the MAF/AFM or airbox avoids contaminating sensors and gives room to work. Labeling avoids vacuum/connector routing errors that cause drivability faults.

3) Isolate and plug ports
- Before opening the intake to the head, plug the runner openings with clean shop towels or suitable caps to prevent grit and liquid from entering the intake ports/cylinders.
Theory: Prevents debris from falling into cylinders where it could damage valves/pistons or be inhaled by the engine.

4) Remove upper intake plenum (and lower if necessary for full access)
- Unbolt the plenum and lift it clear. Inspect intake gasket surfaces and condition of gaskets, PCV valve, and EGR passages. Replace gaskets during reassembly.
Theory: Proper cleaning requires direct access to runner surfaces and throttle bores. Damaged or leaking gaskets are a common cause of vacuum leaks and must be replaced to restore sealing and correct air metering.

5) Inspect and assess carbon severity
- Light varnish vs heavy hard carbon: determines cleaning method. Light deposits can be dissolved with solvent and brushing; heavy deposits on valves may require walnut‑blasting or professional media cleaning.
Theory: Hard compacted carbon (especially on valves or in narrow ports) cannot be removed safely with solvent/brush alone; abrasives restore physical cross‑section without aggressive scraping that could damage mating surfaces.

6) Clean the plenum, runners, throttle body, IAC (idle control) and EGR/PCV passages
- Use a dedicated intake/throttle cleaner and non‑metal brushes, scrapers or nylon brushes. For throttle bodies, spray cleaner and move butterfly to clean the bore and shaft. Clean IAC passages and the IAC valve body. For plenum/runners, use brushes and solvent, finish with compressed air (blow away debris into a shop rag). Replace PCV valve. For heavy valve deposits consider walnut‑blasting of ports/valves (performed with manifold off).
Theory: Removing deposits restores original cross‑section and smoothness of airflow. Throttle and IAC cleaning restores precise control of idle air; EGR/PCV cleaning removes flow restrictions and stops extra oil/soot input. Walnut blasting abrasively strips carbon from valve faces without removing metal, restoring sealing and air flow at the port/valve interface.

7) Clean sensors and mating surfaces
- Gently clean MAF (if removed) with dedicated MAF cleaner; clean throttle position sensor connectors and all gasket surfaces. Ensure no solvent enters sensors.
Theory: Sensors must read clean airflow/position signals; contamination or residue changes sensor outputs and causes incorrect fueling/idle control.

8) Reassemble with new gaskets and proper torque
- Replace intake/plenum gaskets, throttle body gasket, and any o‑rings. Reinstall components in reverse order, reconnect vacuum lines and electrical connectors. Torque bolts to factory specs (consult service manual).
Theory: New gaskets restore sealing; correct torque avoids vacuum leaks and stress that lead to warpage or leaks which would replicate the original fault.

9) ECU and idle relearn
- Reconnect battery, clear codes, and allow ECU to relearn idle (idle at normal operating temperature, follow manufacturer relearn if required). Test at idle and under load.
Theory: After changing airflow characteristics and replacing sensors/gaskets, the ECU adaptation values (idle integrators, fuel trims) will be out of spec; clearing and relearning lets the ECU re‑establish correct fueling and idle control.

10) Verification
- Road test and monitor for return of symptoms. Check for vacuum leaks, scan for codes, monitor fuel trims and idle stability. If symptoms persist, investigate additional causes (vacuum leaks, faulty IAC, intake manifold runner control actuators, injector problems).
Theory: Confirms that restored airflow and sealing returned the engine to correct air/fuel and idle control behavior.

How the repair fixes the fault (theory summary)
- Restoring flow area: Cleaning removes deposits that narrow runners and plenum cross‑section, so airflow to each cylinder becomes closer to the calibrated design. This reduces local lean/rich conditions and improves volumetric efficiency and power.
- Reestablishing symmetry and boundary conditions: Carbon alters airflow patterns and creates turbulence and flow imbalance between cylinders; cleaning evens airflow distribution so mixture and combustion become consistent cylinder‑to‑cylinder.
- Idle control accuracy: Throttle bore deposits and clogged IAC passages cause incorrect bypass airflow, producing rough/hunting idle. Cleaning restores the controlled bypass and throttle movement so idle control algorithms work properly.
- Sensor integrity and vacuum sealing: Cleaning sensors and replacing gaskets/PCV reduces false sensor readings and vacuum leaks that drive incorrect fuel trims and spark advance.
- Valve and sealing restoration: When valve faces or seats are coated, sealing and heat transfer are impaired; removing carbon restores valve sealing and combustion chamber conditions, reducing misfires and improving efficiency.

When to escalate / alternatives
- If valves have heavy hard carbon: walnut blasting (OEM‑approved) or professional service is preferred. If intake manifold runners or actuators are broken, replace rather than clean. If repeated re‑fouling occurs, investigate PCV system or oil consumption.

Concise cautions
- Do not spray solvent into open cylinders. Avoid getting abrasive or solvent into sensors. Use proper torque specs and new gaskets. Follow shop manual for any model‑specific steps.

This sequence restores proper airflow paths, sealing and sensor readings so the engine returns to correct air/fuel metering, stable idle and normal performance.
rteeqp73

Mitsubishi DOHC V6 (6G72) Service Highlights Explanation of the Mitsubishi DOHC V6.

6G72 Engine Diagnostics - Rough Idle and Stalling In this video I take you through testing the Throttle Position Sensor and Idle Air Control Valve. I talk about the symptoms that they ...

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- Safety first
- Wear safety glasses, nitrile gloves, and work in a well ventilated area.
- Disconnect the negative battery cable before starting electrical work.
- Allow the engine to cool fully before draining coolant or opening the cooling system.
- Use a floor jack with rated jack stands on level ground and wheel chocks; never rely on the jack alone.
- Keep a fire extinguisher nearby when working on fuel or electrical systems.

- Required reference
- Obtain the factory service manual (FSM) or a good Haynes/Chilton manual for the Mitsubishi 6G72 for exact torque values, bolt sequences, timing specs, and illustrations. Do not guess torque or timing specs.

- Basic tool list (describe each tool and how to use it)
- Metric socket set (3/8" and 1/2" drive; 8–24 mm typical range)
- What it is: sockets that fit over nuts/bolts.
- How to use: attach socket to ratchet or breaker bar, select correct size for the fastener, pull or push the ratchet handle to loosen/tighten. Use correct drive size for force needed.
- Ratchet (3/8" and preferably 1/2" drive)
- What it is: a handle that drives sockets with a reversible ratchet mechanism.
- How to use: set ratchet direction, attach socket, use for routine loosening/tightening.
- Breaker bar (long, non-ratcheting)
- What it is: a long fixed bar used for heavy loosening.
- How to use: use when bolts are seized or very tight; apply steady force rather than jerking.
- Torque wrench (click-type, appropriate range to cover head bolts)
- What it is: tool that applies a precise torque.
- How to use: set required torque, tighten bolt until wrench “clicks” (or indicates). Use for head bolts, manifold bolts, and critical fasteners. Always re-zero to lowest setting before storage.
- Torque angle gauge (or electronic torque/angle tool) — required if bolts are torque-to-yield (angle-tightening)
- What it is: measures the angle of rotation after an initial torque.
- How to use: used following the factory procedure when final steps require turning bolts a specific number of degrees.
- Extension bars and universal joint (U-joint)
- What it is: extensions that let you reach recessed fasteners and flex joints.
- How to use: attach between ratchet and socket as needed to reach awkward bolts.
- Combination wrenches (metric)
- What it is: open-end and box-end wrenches in one tool.
- How to use: useful for bolts where a socket won’t fit; use the box end for better grip on rounded fasteners.
- Screwdriver set (flat and Phillips)
- What it is: for clamps, small screws, prying lightly.
- How to use: use correct tip and size to avoid stripping.
- Pliers (regular, needle-nose, locking/vice grips)
- What it is: gripping tools for clips, clamps, hoses.
- How to use: use needle-nose for small clips and connectors; locking pliers for stubborn parts (with care).
- Hose clamp pliers or pliers with locking feature
- What it is: for spring-style hose clamps.
- How to use: compress clamp, hold open, remove hose.
- Spark plug socket with swivel and extension
- What it is: deep socket with rubber insert to hold plug.
- How to use: remove/install spark plugs without dropping them.
- Drain pan and funnels
- What it is: collects fluids and funnels for refilling.
- How to use: drain coolant/oil into pan and dispose/recycle appropriately.
- Gasket scraper and plastic scrapers
- What it is: tools to remove old gasket material.
- How to use: scrape gently to avoid gouging aluminum surfaces; use plastic scraper for final cleaning.
- Wire brush and brake cleaner or solvent
- What it is: cleans metal surfaces and removes corrosion/deposits.
- How to use: clean mating surfaces and fasteners; keep solvents away from rubber parts.
- Shop rags and vacuum
- What it is: rags for cleanup and vacuum to remove debris.
- How to use: cover open cylinders with rags and vacuum debris to avoid contamination.
- Jack and jack stands (rated)
- What it is: lifts the vehicle and supports it.
- How to use: use jack to lift, place stands under recommended lift points, lower onto stands.
- Engine hoist, engine support bar, or at least one strong helper
- What it is: supports/lifts cylinder head or engine components during removal.
- How to use: use hoist to lift heavy cylinder head safely; head is heavy and awkward — don’t try alone without a proper lift or another person.
- Camshaft locking tool/timing tool kit for 6G72 (special service tool)
- What it is: holds cams/engine at correct timing alignment when removing/installing timing belt/camshafts.
- How to use: install per FSM to prevent cam rotation and keep valve timing.
- Harmonic balancer/ crank pulley puller (if crank pulley must come off)
- What it is: pulls pressed-on pulley from crankshaft.
- How to use: attach to pulley and pull evenly to avoid damage.
- Straightedge and feeler gauges
- What it is: checks block/head flatness (warpage).
- How to use: place straightedge across mating surface and measure gaps with feeler gauges; acceptable limits in FSM.
- Feeler gauges and small metric calipers (optional)
- What it is: measure clearances/confirm valve lash if needed.
- How to use: measure as directed for valve preload/clearance checks.
- Magnetic pickup tool and parts tray
- What it is: retrieves dropped fasteners and organizes bolts.
- How to use: use magnetic tool to pick items; keep bolts labeled and organized.
- Compression tester (optional but helpful)
- What it is: checks cylinder compression before and after repair.
- How to use: remove plugs, screw tester in, crank engine to read pressure. Helps confirm head gasket and valve condition.

- Extra/specialty tools and why they’re required (if you don’t have them)
- Torque wrench and torque angle gauge
- Why required: head bolts must be tightened to specific torque/angle in the correct sequence. Incorrect torque risks leaks or broken bolts.
- Camshaft locking/timing tool kit for 6G72
- Why required: prevents camshafts from rotating and losing timing; avoids valve-piston contact and catastrophic engine damage.
- Engine hoist/support or extra hands
- Why required: cylinder heads are heavy and awkward; safe lifting prevents injury and component damage.
- Harmonic balancer puller
- Why required: crank pulley may be pressed on; forcing it off will damage the crank if you don’t use a proper puller.
- Straightedge/feeler gauges or machine-shop inspection
- Why required: to check head/block flatness and avoid reusing a warped head gasket surface. Machine shop services are recommended for accurate measurements.

- High-level procedure (follow FSM for exact steps, torque specs, and sequences)
- Prepare: disconnect battery, drain coolant into pan, remove air intake and battery for space, label hoses/electrical connectors with tape/marker or take photos.
- Remove accessories in the way: alternator, A/C compressor (support A/C if you don’t disconnect lines), power steering pump (support lines), drive belts.
- Remove intake and exhaust manifolds: remove manifold bolts and gaskets; keep bolts organized and mark which bank they came from.
- Remove valve covers and accessory components: remove spark plug wires/ignition coils and set aside.
- Set engine to TDC for cylinder 1 and mark timing belt/chain position: mark belt and sprocket positions with paint/marker or use cam lock tool. NEVER rely on marks alone if you’re unsure — use cam locking tools.
- Remove timing belt/chain and associated covers: follow FSM for timing removal. Keep the belt orientation if reusing (not recommended) and note routing.
- Remove camshafts/rockers (if required by your head design) following FSM: keep cam journals and caps in order; mark everything carefully.
- Loosen head bolts gradually in the reverse order of the tightening sequence to avoid warping. Use breaker bar then finish removing with ratchet.
- Lift the head off with an assistant or hoist, keeping it level; place on a clean surface.
- Inspect head and block:
- Clean and inspect mating surfaces for cracks, coolant passage erosion, or burn-through.
- Check for warpage with a straightedge and feeler gauge; compare to FSM tolerances.
- Pressure-test head at a machine shop to check for cracks between coolant and oil passages.
- If head is warped or cracked:
- Take head to a machine shop for resurfacing and pressure testing. Resurfacing may change required gasket thickness; consult FSM.
- Replace head or block if cracks are severe or machining cannot restore spec.
- Clean block deck and head mating surface:
- Remove all gasket material carefully with plastic scraper and solvent, avoid letting debris fall into coolant passages or cylinders; cover cylinders with rags or use vacuum.
- Install new head gasket (use OEM or quality aftermarket)
- Ensure correct orientation and proper placement; check for dowel pins alignment.
- Install head and new head bolts if required:
- If bolts are torque-to-yield (check FSM), replace them. If reusable bolts are allowed, follow FSM re-use guidance.
- Tighten in the exact sequence and steps: initial snug, incremental torque steps, then final angle steps if required.
- Reassemble camshafts/valvetrain and set timing:
- Use cam locking tools and follow timing belt tensioning procedure; rotate engine by hand twice and re-check timing marks.
- Reinstall intake/exhaust manifolds with new gaskets, valve covers, accessories, belts, and pulleys.
- Replace fluids: new oil and oil filter, new coolant (use correct mixture), bleed cooling system per FSM.
- Reconnect battery, start engine, and check for leaks, unusual noises, or smoke. Monitor coolant and oil levels and do a compression or leak-down test if desired.

- Parts commonly replaced during a head gasket job and why
- Head gasket(s) (required)
- Why: original gasket has failed; must be replaced with new OEM-quality gasket sized for the 6G72.
- Head bolts (often required)
- Why: many head bolts are torque-to-yield and must be replaced because they stretch. Check FSM; replacing head bolts avoids failure.
- Valve cover gaskets and intake/exhaust manifold gaskets (recommended)
- Why: removed during disassembly and often brittle; replacement prevents future leaks.
- Timing belt, tensioner, idler pulleys, and water pump (strongly recommended)
- Why: these are exposed when removing timing components; if they fail later it can cost another head job. Replace as preventive maintenance, especially if age/mileage is unknown.
- Camshaft seal(s) and crankshaft seal(s) (recommended)
- Why: seals are accessible and commonly replaced to prevent oil leaks afterward.
- Thermostat and coolant hoses (recommended)
- Why: cooling system was drained; new thermostat and hoses reduce risk of overheating and future coolant leaks.
- Spark plugs (recommended)
- Why: accessible and inexpensive; replace while heads are off or during reassembly.
- Oil and oil filter (required)
- Why: oil will be contaminated with coolant; change after repair.
- Coolant (required)
- Why: system was drained; refill with correct mix and bleed air.
- If head is warped/cracked: resurfacing or replacement of the head, and possibly new valves/seals or valve work (as recommended by machine shop).

- Critical checks and checks to send to a shop
- Have the cylinder head pressure-tested for cracks (machine shop).
- Have the head deck checked for flatness and resurfaced if out of spec.
- If valves or valve guides are worn, the machine shop should inspect and repair or you’ll see oil burning/compression issues.

- Common pitfalls and warnings
- Do not skip the service manual torque/sequence/angle steps — improper tightening causes leaks or broken bolts.
- Do not allow debris into cylinders or coolant passages — cover openings and vacuum thoroughly.
- Never reuse a torque-to-yield head bolt.
- If you’re not 100% confident with timing belt/cam timing, get professional help — incorrect timing can destroy the engine.
- Expect this job to take a weekend (or multiple days) for a beginner; don’t rush.

- Testing after reassembly
- With new gasket and new fluids, run engine to operating temperature and check for coolant and oil leaks.
- Monitor for white smoke (coolant burning) or milky oil (coolant in oil).
- Perform a cooling system pressure test for leaks.
- After a few hundred miles, re-torque accessible bolts per FSM if required and recheck fluids.

- Final recommendation (no fluff)
- Get the FSM for the 6G72, invest in a torque wrench and cam locking/timing tools, have the head inspected/resurfaced at a machine shop, and replace timing belt/water pump while you’re in there. If you lack the cam-locking tools or a second experienced person, have a shop or experienced mechanic perform or supervise the timing/cam steps.
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