H4D: Cleaning throttle body without dismantling

Introduction

Applies to H4D engine only.

This is a simple method of cleaning the throttle body without removing it. It is sufficient in most cases and offers remarkable results. Because of its simplicity and the short time it takes, it is advisable to carry out this operation every time the air filter is changed.

The vehicle must be on a slight upward slope or slightly elevated so that the front is tilted upwards and the rear (engine) is tilted downwards.

The aim is to allow fluid and impurities to drain naturally from the throttle body.

What you need

Step 1 Accessing the engine hood

H4D: Cleaning throttle body without dismantling, Accessing the engine hood: step 1, image 1 of 1

Open the trunk.
Put aside the trunk carpets.

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Step 2 Acessing the engine compartment

H4D: Cleaning throttle body without dismantling, Acessing the engine compartment: step 2, image 1 of 1

Unscrew the 6 T50 screws by hand or using a wrench and a socket.
Lift and put aside the engine hood.

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Step 3 Remove the air filter housing

H4D: Cleaning throttle body without dismantling, Remove the air filter housing: step 3, image 1 of 2

H4D: Cleaning throttle body without dismantling, Remove the air filter housing: step 3, image 2 of 2

Using a screwdriver, loosen the two Torx T25 screws on the air filter cover.
Remove the cover by moving it forward and then lifting it.

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Step 4 Clear the air duct

H4D: Cleaning throttle body without dismantling, Clear the air duct: step 4, image 1 of 2

H4D: Cleaning throttle body without dismantling, Clear the air duct: step 4, image 2 of 2

Disconnect the oil vapour breather.
Loosen the hose clamp on the pipe leading to the throttle body using a flathead screwdriver.
Remove the pipe and airbox cover. Set the filter aside if it is to be used again later.

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Step 5 Cleaning the throttle valve

H4D: Cleaning throttle body without dismantling, Cleaning the throttle valve: step 5, image 1 of 3

H4D: Cleaning throttle body without dismantling, Cleaning the throttle valve: step 5, image 2 of 3

H4D: Cleaning throttle body without dismantling, Cleaning the throttle valve: step 5, image 3 of 3

Spray brake or contact cleaner on the throttle and use a soaked paper towel to clean it until the body and edges are clean.
It is recommended to wear gloves while handling the break cleaner.
Allow to dry for a few minutes before refitting the airbox.
When the ignition is switched on, the throttle valve defaults to the idle position, but it can be opened fully by holding the accelerator pedal to the stop.
If the accelerator pedal is released, even slightly, the throttle will close, risking cuts to fingers and damage to the gearbox motor!

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Step 6 Refitting the airbox

Replace the pipe as far as it will go.
Tighten the clamp screw with a flathead screwdriver while holding the pipe in its correct position.
Reinstall the air filter.
Replace the cover by sliding it towards the notches.
Re-tighten the two Torx T25 screws while maintaining slight pressure on the cover.

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Step 7 First restart

The first restart after cleaning is likely to fail and/or require many, many revolutions of the starter motor, even if the engine is warm!
Depending on the initial level of contamination, the ECU needs to reset itself to a completely different idle position from the one it recorded just before. It may take a few moments to recalibrate itself automatically.

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Step 8 Road test and expected results

Once the engine is stable, carry out a test drive. The results presented below are ideal and there is no guarantee that all of them will be achieved.
Engine behaviour, particularly at low revs and idling, may become smoother. The idle speed may drop more quickly and become more stable.
Vibrations are reduced when restarting at stop signs, red lights and when maneuvering on wet/icy roads.
Better engine response when the clutch is re-applied and during restart: beneficial for heel-toe shifting.
This operation reduces clutch wear during any operations involving the clutch.