DIY Lexus Is Performance Intake Installation: Step-by-step with Milltek and Injen Kits

Introduction: Unlocking Your Lexus IS Performance Potential

Upgrading to a high-flow intake system is one of the most rewarding modifications you can make to your Lexus IS. A performance intake replaces the restrictive factory airbox, reducing intake restriction and allowing the engine to breathe more freely. The result is a noticeable increase in throttle response, a modest horsepower gain (typically 5–15 hp depending on the model and tune), and a more aggressive intake sound that transforms the driving experience. This guide provides a comprehensive, step-by-step approach to installing two popular aftermarket intake kits—Milltek and Injen—on a Lexus IS platform. Whether you drive an IS250, IS350, or a later model, the general principles remain the same, though minor variations in engine bay layout may require adapters specific to your vehicle. We’ll cover everything from tool selection to final testing, ensuring a professional-quality install in your home garage.

Tools and Materials Needed

Before you begin, gather the following tools and safety gear. Having everything at hand will prevent interruptions and keep the process smooth.

Socket set – 3/8” drive with standard and deep sockets (10mm, 12mm, 14mm are most common)
Wrench set – combination wrenches (10mm, 12mm, 14mm)
Screwdriver set – Phillips head and flathead
Torque wrench – for tightening bolts to manufacturer specifications
Performance intake kit – Milltek or Injen, specific to your Lexus IS engine and year
Rubber gloves – to keep oily hands off the new filter
Shop towels – for cleaning and wiping up oil
Zip ties – for securing silicone hoses or vacuum lines if needed
Masking tape or marker – to label connectors and hoses
Optional: OBD-II scanner – to later confirm no check engine lights

Preparation and Safety

Park on a level surface – Engage the parking brake and leave the car in Park (automatic) or first gear (manual).
Allow the engine to cool – A hot engine increases burn risk and makes intake components difficult to handle.
Disconnect the negative battery terminal – This prevents accidental shorting and resets the ECU, which will adapt to the new airflow after installation.
Gather your tools – Lay them out within easy reach.
Read the included instructions – Though this guide is comprehensive, each kit may have unique steps; refer to the manufacturer’s manual for torque values.

Removing the Stock Intake

The factory intake on a Lexus IS is clamped and bolted in several places. Removing it carefully will save time later. Follow these steps for a clean removal.

Open the hood – Prop it securely. Locate the intake system: the airbox sits near the passenger-side engine bay with a large plastic duct leading to the throttle body.
Disconnect the MAF sensor (Mass Airflow) – Unplug the wiring connector from the MAF housing. Use a small flathead screwdriver to release the tab if necessary. Place the sensor aside safely.
Loosen air duct clamps – Use a flathead or socket to loosen the clamp connecting the intake tube to the throttle body. Also loosen any clamps attaching the intake tube to the airbox.
Unbolt the airbox – There are typically two or three 10mm bolts at the bottom of the airbox. Remove them and set them aside.
Lift the airbox out – Gently wiggle the airbox upward, tilting it to clear the strut brace (if equipped) and other components. Be careful not to damage any nearby hoses.
Remove the intake tube – Pull the intake tube free from the throttle body. Plug the throttle body opening with a clean shop towel to prevent debris from entering.
Inspect the old filter – Note how dirty it is; a dirty stock filter can cost you power and MPG. Dispose of the old filter and airbox properly (some plastic can be recycled).

Milltek Intake Installation: Step-by-Step

Milltek’s intake system is known for its precision engineering, CNC-machined aluminum tubing, and a high-flow cotton/gauze filter. It typically uses OEM mounting points for a hassle-free install.

Unpack the Milltek kit – Verify you have the main intake tube, heat shield (if included), filter, clamps, couplers, mounting brackets, and hardware. Some IS kits include a separate cold-air intake.
Install the heat shield – If your Milltek kit includes one, position it into the engine bay where the old airbox sat. Use the provided bolts to secure it to the chassis holes. This shield protects the filter from engine bay heat.
Attach the intake tube to the throttle body – Slide the provided silicone coupler onto the throttle body opening. Place the aluminum intake tube into the coupler and tighten the clamps. Do not overtighten – just snug enough to seal without collapsing the tube.
Mount the intake tube – The tube will route toward the front or passenger side, depending on the specific IS model. Use the supplied bracket (if any) to bolt the tube to existing studs or bolts. Ensure the tube does not contact any hot surfaces (e.g., radiator hose or engine block).
Install the filter – Slide the cone filter onto the end of the intake tube. Tighten the clamp securely. Verify the filter sits inside the heat shield (if used).
Reconnect the MAF sensor – Many Milltek kits relocate the MAF sensor into the new intake tube. Carefully unscrew the MAF sensor from the old housing and install it into the bung on the Milltek tube. Ensure the sealing O-ring is seated. Tighten the screws to avoid vacuum leaks. Then plug the electrical connector back in.
Secure all loose hoses – Some IS models have a small idle air control hose or crankcase vent line. Use the included barb fittings or zip ties to attach these to the new intake. Cross-reference with the original configuration.
Double-check all clamp positions – Ensure no clamp is obstructing the throttle body movement or hitting the hood when closed.
Reconnect the negative battery terminal – You are now ready to test.

Injen Intake Installation: Step-by-Step

Injen’s kits are among the most popular, especially the Injen SP (Short Ram) or Injen Evolution (Cold Air) lines. The installation shares many steps with Milltek, but Injen often uses a black powder-coated tube and a lifetime washable filter. Below are the specifics for a typical Lexus IS Injen intake.

Lay out the Injen components – You will find a polished or coated intake tube, a cotton filter, silicone couplers, clamps, a mounting bracket, and a heat shield in some versions. Injen cold-air intakes also include an extension tube for the lower bumper area.
Prepare the engine bay – Remove any leftover ducting from the stock system. Clean the throttle body opening with a clean cloth. If you have an Injen cold-air kit, you may need to temporarily remove the front wheel, fender liner, or under-tray to route the lower tube.
Install the heat shield (if included) – The Injen shield often comes with a rubber seal along the top to seal against the hood. Bolt it in place using the supplied hardware and the factory airbox mounting points.
Mount the intake tube – Start by loosely attaching the tube to the throttle body using the supplied silicone coupler. On Injen kits, the tube may also use a bracket that bolts to the studs where the old airbox bracket was attached. Do not fully tighten yet.
Connect the lower tube (cold air only) – If installing an Injen Evolution cold-air intake, connect the second tube that extends down into the front bumper. Slide a coupler between the two tubes. Route the lower tube carefully to avoid the power steering lines or radiator fan. Secure with the provided clamps.
Install the filter – For a short ram, the filter attaches directly to the upper tube. For cold-air intakes, the filter is at the bottom of the lower tube. Ensure it is clear of any water splash concerns – Injen provides a hydro-shield sleeve to reduce water ingestion. Inspect the installation area: it should be behind the bumper but above the lower control arm.
Transfer the MAF sensor – The Injen tube has a dedicated MAF flange. Carefully remove the MAF sensor from the old intake and install it onto the new tube. Apply a tiny amount of dielectric grease to the connector pins to prevent corrosion. Secure with the screws.
Reconnect any vacuum lines – Injen kits usually include a small fitting for the crankcase vent. Connect the hose and secure with a zip tie.
Tighten all clamps and brackets – Now go back and torque each clamp. Use a torque wrench if possible; most silicone coupler clamps require 4–6 ft-lbs. Ensure the intake tube clears nearby components by at least 1/4 inch.
Reconnect the battery – You are ready for test fire.

Comparing Milltek and Injen: Which Is Right for Your Lexus IS?

Both kits deliver a meaningful performance upgrade, but they differ in philosophy and design. Consider the following:

Build Quality – Milltek uses high-grade TIG-welded aluminum with a durable black powder coat. Injen tubes are typically polished or metallic powder-coated. Both are excellent.
Filter Design – Milltek uses an oiled cotton filter (like K&N). Injen uses its proprietary cotton media. Both require periodic cleaning and re-oiling.
Sound – Milltek intakes tend to produce a slightly deeper induction growl, while Injen units are a bit more pronounced during hard throttle. Neither is too loud for daily driving.
Heat Shield Effectiveness – Milltek’s shield is often a full metal shroud with a rubber seal. Injen’s shield is similar but sometimes an add-on for short ram versions. If you live in a hot climate, consider an intake with a comprehensive heat shield.
Price – Injen kits are generally more affordable ($300–$400), while Milltek is premium ($400–$600).
Emissions – Both are 50-state legal (CARB EO numbers vary by model; check your specific kit).

For daily drivers and first-time installers, either kit is an excellent choice. If you are chasing every last horsepower on a tuned IS, Milltek’s more consistent airflow properties may edge ahead. For the budget-conscious enthusiast, Injen offers great value and proven gains.

Final Checks and Testing

After installation, do not simply drive away. Perform these critical checks to ensure the intake is safe and functioning properly.

Inspect all connections – Visually verify that every clamp is tight, no couplers are twisted, and the intake tube is not touching the radiator hose or engine block.
Check for air leaks – With the engine idling, listen for any hissing or whistling sounds. A small leak can cause a lean condition and potential drivability issues. Use a spray bottle with soapy water on all connections; bubbles indicate a leak.
Verify MAF sensor wiring – Ensure the connector is fully seated. If you accidentally damaged the sensor during installation, replace it before driving.
Test drive – Take a 10–15 minute drive through varying speeds. Pay attention to throttle response – it should be sharper and more immediate. The intake sound will change, especially between 2,500–4,500 RPM. No check engine light should appear.
Re-torque after a week – Vibration can loosen clamps. After 100 miles, recheck all bolts and clamps.

Long-Term Maintenance and Care

To keep your performance intake delivering gains, follow these maintenance guidelines:

Clean the filter every 5,000–10,000 miles – More often if you drive in dusty or sandy conditions. Use a dedicated filter cleaning kit (e.g., K&N cleaner or Injen’s own kit).
Re-oil sparingly – Over-oiling can foul the MAF sensor, leading to poor idle and hesitation. Apply oil evenly and allow it to dry for an hour before reinstalling.
Inspect silicone couplers – Over time, heat cycles can dry them out. Replace if cracked or hardened.
Check heat shield sealing – Rubber seals may degrade; a new seal will keep hot air out.

Conclusion

Installing a performance intake on your Lexus IS is a straightforward Saturday project that delivers immediate gratification. Whether you choose the refined engineering of Milltek or the proven performance of Injen, the process is rewarding and the results are tangible. You will enjoy sharper throttle response, a more engaging engine note, and the satisfaction of working on your own car. Follow the steps outlined above, take your time, and enjoy the upgrade. For further reading and product-specific information, visit Milltek’s official site or Injen Technology’s homepage. For community support, check out the Club Lexus forums for installation tips and owner experiences.