DIY Guide: Toyota Tacoma/4Runner 1999-2004) 3.4L

If you are driving a 1999-2004 Tacoma or 4Runner with the 3.4L 5VZ-FE, you have one of the most reliable engines ever made. However, Toyota designed the factory intake for quietness, not performance.

Unlike the older T-100s, your truck uses a modernized electronics system. This guide is specifically written for the 1999-2004 Drop-In MAF Sensor configuration. Follow these steps to unlock better throttle response and that signature deep intake growl.

Phase 1: The Setup

Time Estimate: 60–90 Minutes
Difficulty: 2/10 (Beginner Friendly)

Tools Required:

• Ratchet with 10mm and 12mm sockets
• Extensions (6-inch)
• Phillips Head Screwdriver (Ideally JIS standard, but a good #2 Phillips works)
• Needle Nose Pliers
• Silicon Spray or WD-40 (to help couplers slide on)

Safety First: Disconnect the Negative (-) Battery Terminal. This resets the ECU fuel trims and protects the sensitive MAF sensor electronics.

Phase 2: The Teardown

Step 1: Unplug the MAF Sensor

Locate the electrical connector on the airbox (driver's side). Squeeze the tab, pull the plug off, and tuck the wire harness safely out of the way.

Step 2: Remove the "Silencer" Resonator

This is the black plastic box sitting along the intake tube near the engine.

1. Disconnect the vacuum hoses attached to the back of the resonator (Fuel Pressure Regulator & PCV).
2. Loosen the hose clamps at the throttle body and the airbox.
3. Remove the two 10mm bolts holding the resonator to the engine brackets.
4. Pull the entire tube assembly off the throttle body.

Step 3: Remove the Factory Airbox

Undo the three 12mm bolts holding the bottom of the airbox to the inner fender. Lift the entire box out of the engine bay.

Phase 3: The Surgery (MAF Transfer)

Step 4: Extract the MAF Sensor

Locate the two small screws holding the sensor bulb into the plastic tube. Unscrew them and gently pull the sensor straight out.

Check the O-Ring: Ensure the rubber O-ring is still on the sensor. If it's stuck in the old box, fish it out and put it back on the sensor.

Step 5: Install MAF into New Tube

Your new CAI tube has a machined slot for this sensor.

• Insert the sensor carefully.
• Direction: The "bulb" (diode) usually faces into the airflow, and the solid plastic side faces the engine.
• Use the new screws provided with the kit. Do not over-tighten; the housing is aluminum and strips easily.

Phase 4: Installation

Step 6: Install the Heat Shield

Place the new metal heat shield into the corner where the old airbox was. Bolt it down using the original factory 12mm holes in the fender. Install the rubber weather stripping on top to seal against the hood.

Step 7: Throttle Body Coupler

Install the silicone coupler onto the engine throttle body.

Tip: While the tube is off, wipe the inside of the throttle body butterfly valve with a clean rag to remove carbon buildup.

Step 8: Install the Main Intake Tube

Slide the new tube (with the MAF sensor now installed) into the throttle body coupler. Connect the other end to the filter adapter/heat shield. Do not tighten clamps yet—adjust the rotation so the tube clears the brake lines and fan shroud.

Step 9: Vacuum Lines (Don't Forget These!)

• Fuel Pressure Regulator (FPR): Connect the small line from the fuel rail to the small nipple on the intake tube.
• PCV Valve: Connect the larger hose from the valve cover to the large nipple on the intake.
• Ensure these hoses are not kinked or pinched.

Step 10: Final Tightening

Once everything is aligned, tighten all hose clamps (Throttle body, MAF side, Filter side). Plug the electrical harness back into the MAF sensor.

Phase 5: The Test

1. Reconnect Battery: Hook up the Negative terminal.
2. Start the Engine: The truck might stumble or idle high (1500 RPM) for a few seconds. This is normal as the ECU relearns air density.
3. Check Engine Light? If a light comes on immediately, check that the MAF sensor is plugged in and facing the right direction.
4. Listen: Give the throttle a blip—you should hear a deep "whoosh" sound.