Introduction

A cold air intake is one of the most popular and cost-effective modifications you can make to a Mitsubishi Eclipse. By drawing cooler, denser air from outside the engine bay, an AEM cold air intake can improve throttle response, increase horsepower, and enhance fuel efficiency when paired with proper tuning. The AEM intake system is engineered with powder-coated aluminum tubing, a high-flow air filter, and precision-fit hardware specifically for the Eclipse chassis. This guide walks through the entire installation process with enough detail to get the job done right the first time, whether you are working on a 2G (1995–1999) or 3G (2000–2005) model. Always cross-reference your specific AEM kit number with the included manual for any model-specific variations.

Tools and Materials Needed

Before starting, gather everything required. Having the correct tools on hand prevents frustrating interruptions and ensures you do not damage any components.

Required Items from the AEM Kit

  • AEM cold air intake kit (part number varies by Eclipse generation and engine)
  • High-flow dry or oiled air filter (pre-oiled if using AEM DryFlow)
  • Heat shield or cold-air box (included with some kits)
  • Hose clamps, silicone couplers, and mounting brackets
  • Mass air flow sensor (MAF) adapter or mounting gasket

Hand Tools

  • Socket wrench set (metric sizes: 8mm, 10mm, 12mm, 14mm)
  • Flathead screwdriver (medium and large)
  • Phillips-head screwdriver (#2)
  • Ratchet with 3-inch and 6-inch extensions
  • Torque wrench (inch-lbs for small bolts, ft-lbs for larger)
  • Pliers (slip-joint and locking)
  • Allen key set (hex keys) – some kits use hex bolts

Consumables and Safety Gear

  • Shop towels or rags
  • Safety glasses
  • Mechanics gloves
  • Thread locker (medium strength, blue Loctite)
  • Silicone spray or anti-seize for oxygen sensor (if needed)
  • Zip ties (various sizes) for wire management
  • Penetrating oil (for stubborn bolts on older vehicles)

Optional Diagnostic Tools

  • OBD-II scanner to clear codes and monitor intake air temperature
  • Digital multimeter (to verify MAF sensor voltage after installation)
  • Vacuum gauge (to check for post‑MAF air leaks)

Preparation and Safety

Work in a well‑ventilated area with plenty of light. If you are parking on a slope, chock the wheels. Disconnect the negative battery terminal using a 10mm socket and wrap the cable end with a rag to prevent accidental contact. Wait at least five minutes after disconnecting before touching any airbag or sensor wiring. Clear your engine bay of debris—leaves, dirt, or loose parts can cause issues once the intake is opened.

Check your vehicle’s service manual for any special procedures, especially if you have an aftermarket ECU or turbocharged Eclipse (e.g., Eclipse GSX or GST models). This guide assumes a naturally aspirated 4G64 or 4G63 engine, but the general steps apply to most Eclipse platforms with minor routing differences.

Step 1: Remove the Factory Intake System

Taking off the stock air intake is straightforward, but you must work carefully to avoid damaging the mass air flow sensor or any plastic connectors.

Disconnect the MAF Sensor

Locate the mass air flow sensor between the air filter box and the intake tube. It is held in place with two Phillips screws or small bolts. Unplug the wiring harness by pressing the release tab and pulling straight back—do not twist or pry. Set the sensor aside in a clean, static‑free area.

Remove the Air Filter Box

Use a socket wrench (usually 10mm or 12mm) to remove the bolts securing the lower and upper halves of the factory air box. Some Eclipse models have a resonance chamber or additional ducting that may need to be unfastened. Lift out both halves and set them aside. If the rubber grommets are brittle, replace them to avoid future rattling.

Detach the Intake Tubing

Loosen the hose clamps on the rubber couplers connecting the intake tube to the throttle body and to the MAF housing. Gently twist and pull the tube free. On some models, a bracket supports the tube near the engine mount—remove this with a 12mm socket. Check the old tubing for any built‑up oil or debris; clean the throttle body opening with a shop towel to prevent anything from falling in.

Clean the Work Area

Before installing the new intake, wipe down the inner fender well and the area around the throttle body. Any dirt or grease that falls into the engine during installation can accelerate wear. Use compressed air if available, but avoid blowing debris toward open intake ports.

Step 2: Install the AEM Cold Air Intake

Lay out all AEM components and compare them to the instruction schematic. The intake tube is typically powder‑coated aluminum—handle with gloves to avoid fingerprints and oils.

Mount the MAF Sensor

Transfer the mass air flow sensor to the AEM MAF adapter using the supplied gasket or O‑ring. Torque the screws to 25–35 in‑lbs if your kit specifies a value. Do not overtighten, as the plastic housing can crack. Ensure the sensor’s arrow aligns with airflow direction (toward the throttle body).

Route and Secure the Intake Tube

Insert the AEM intake tube through the fender well or down toward the lower grille area, depending on whether you are installing a short ram or a true cold air configuration. For a cold air application, the filter will sit behind the bumper or lower valence. Use the included rubber grommets and metal brackets to secure the tube away from moving parts, such as the drive belt and radiator fan. Leave at least 1 inch (25mm) of clearance from hot components like the exhaust manifold and catalytic converter.

Attach the Air Filter

Slip the silicone coupler and hose clamp over the end of the intake tube, then attach the AEM air filter. Position the filter so it is not contacting the inner fender or any sharp metal edges. If your kit includes a heat shield, install it now using the provided hardware. Tighten the hose clamp gently—enough to seal without crushing the filter neck.

Connect the MAF to the Intake Tube

Slide the MAF sensor assembly (with the sensor already mounted) onto the upstream end of the intake tube. Align the divots or indexing marks. Use the supplied hose clamp and tighten to 35–45 in‑lbs. Reconnect the MAF wiring harness—you should hear a click.

Step 3: Secure All Connections and Double‑Check

Air leaks after the MAF sensor will cause lean conditions and poor performance. Go through every connection methodically.

Tighten Clamps in the Correct Sequence

Start at the throttle body coupler, then work to the MAF connections, and finally to the filter. Use a torque wrench for consistency: 35–45 in‑lbs for smaller clamps, 45–55 in‑lbs for larger ones. Avoid pinching silicone couplers unevenly.

Verify Clearance and Routing

Turn the steering wheel full lock left and right to ensure the intake tube does not contact the axle shaft or steering rack. Rev the engine by hand (with ignition off) to check for contact with the throttle cable bracket. Add zip ties to secure any loose wiring or vacuum lines away from the tube.

Reinstall Any Removed Parts

If you previously removed a splash shield or belly pan, reinstall it. The splash guard protects the filter from water splashes and road debris. For lower‑mounted filters, confirm that the drain holes in the fender well are clear to prevent water accumulation.

Step 4: Reconnect the Battery and Reset the ECU

With all connections tight, reconnect the negative battery terminal. Tighten the nut to 10–12 ft‑lbs. The ECU will have lost its learned idle and fuel trims due to the battery being disconnected. Perform an idle relearn procedure:

  1. Start the engine and let it idle without touching the accelerator.
  2. Allow the engine to reach normal operating temperature (coolant at least 180°F / 82°C).
  3. Turn off the engine and wait 30 seconds.
  4. Restart and idle for 2 minutes.
  5. Drive at varying speeds (25–55 mph) for about 10 miles to re‑learn adaptives.

If you have an OBD‑II scanner, clear any stored codes before the first drive. The engine may run slightly rough for a minute or two while the ECU adjusts to the increased airflow.

Step 5: Test the Installation

Start the Eclipse and listen for any unusual sounds—hissing indicates a vacuum leak; whistling may mean a loose clamp or a misaligned MAF gasket. Let the engine idle for several minutes and watch the tachometer; idle should stabilize within ±50 RPM of the stock value (typically 650–750 RPM for a warm engine).

Take a short test drive around the block. Pay attention to:

  • Throttle response – should feel sharper, especially in the mid‑RPM range.
  • Engine smoothness – no surging or hesitation.
  • Check Engine Light (CEL) – if it illuminates, scan for codes. Codes P0171 (lean) or P0101 (MAF circuit) often point to an air leak or improper MAF installation.

After the drive, let the engine cool and re‑tighten all hose clamps. It is normal for silicone couplers to compress slightly after the first heat cycle.

Additional Tips and Maintenance

Performance Gains and Tuning

An AEM cold air intake on a naturally aspirated Eclipse typically adds 5–10 horsepower with no other modifications. If your Eclipse is turbocharged, the gains are larger, but you should also upgrade the bypass valve or recirculation system to keep the MAF sensor reading properly. For maximum benefit, consider a professional ECU tune or a piggyback fuel controller.

Filter Cleaning Schedule

AEM DryFlow filters can be cleaned every 30,000–50,000 miles; oiled filters need re‑oiling after cleaning. Use the official AEM cleaning kit. Never over-oil, as excess oil can contaminate the MAF sensor wire. If your driving environment is dusty, inspect the filter every 10,000 miles.

Avoiding Hydrolock

True cold air intakes that draw air from the lower bumper area are at risk of hydrolock if driven through deep standing water. If your Eclipse is a daily driver in a rainy climate, consider an AEM water‑bypass valve kit. Alternatively, use the supplied heat shield with a directed scoop to keep water away from the filter.

Common Mistakes

  • Overtightening clamps – can crack silicone couplers or deform aluminum tubing.
  • Routing the tube too close to the exhaust manifold – heat soak negates the cold air benefit.
  • Forgetting to plug the MAF sensor back in – the engine will run poorly and may stall.
  • Using oil‑soaked filters without curing – fresh oil deposits can foul the MAF hot wire, causing erratic readings.

Conclusion

Installing an AEM cold air intake on your Mitsubishi Eclipse is a weekend project that rewards you with better throttle response and a more aggressive intake sound. By taking your time with each step—especially the MAF handling, clamp tightening, and ECU relearn—you can ensure a reliable installation that lasts for years. Refer to the official AEM documentation for your specific kit and model year, and don’t hesitate to consult online Eclipse forums for generation‑specific advice. With the intake properly installed, your Eclipse will breathe more freely and deliver the performance you want.

For further reading: AEM Intakes Official Site – product details and installation videos. DSMTuners.com – Mitsubishi Eclipse owners’ forum with thousands of installation threads. MitsubishiForum.com – community discussions for all Eclipse generations.