Why a Trick Flow Throttle Body Upgrade Makes Sense for Your Scion FR-S

The Scion FR-S — along with its Subaru BRZ and Toyota 86 siblings — is already a driver’s car at heart. But the boxer engine’s restrictive intake tract leaves room for improvement. Upgrading to a Trick Flow throttle body is one of the simplest bolt-on modifications that can unlock an honest 10 to 12 wheel horsepower. Trick Flow Specialties, a name trusted in the American performance aftermarket for decades, applies its CNC-porting expertise to the FA20 engine’s throttle body. The result is a larger bore (64mm versus the stock 60mm), smoother airflow, and a more immediate throttle response.

This guide walks you through the complete installation step by step. You’ll learn what tools you need, how to safely remove the factory throttle body, how to prep and install the Trick Flow unit, and what to expect after buttoning everything up. We also cover post-installation considerations, including idle relearn procedures and the potential benefits of a tune. By the end, you’ll be ready to turn the key and feel the difference.

Tools and Materials

Before you pop the hood, gather everything you need. Working without the right tool halfway through is frustrating, and you want to avoid stripping bolts or damaging connectors.

  • Trick Flow Throttle Body — Confirm you have the correct part for the Scion FR-S (TFX part number 85001).
  • 3/8″ drive socket set — You’ll need 10mm, 12mm, and possibly 14mm sockets.
  • Torque wrench (inch-pounds or foot-pounds) — Critical for tightening bolts to spec without cracking the composite intake manifold.
  • Flathead screwdriver — For prying off stubborn hose clamps or connectors.
  • Phillips screwdriver — Some hose clamps use screws.
  • New throttle body gasket — Even if the original looks reuseable, a fresh gasket ensures a leak-free seal. Trick Flow often includes one; have a spare on hand.
  • Throttle body cleaner and lint-free rags — Clean the intake manifold mounting surface thoroughly.
  • Safety glasses and gloves — Throttle body cleaner contains harsh solvents.
  • Small pick tool or trim removal tool — Helps release electrical connector tabs without breaking them.
  • Dielectric grease (optional but recommended) — Apply a thin film to electrical terminals to prevent corrosion.

Preparation and Safety

Park the FR-S on a level surface and let the engine cool completely — at least two hours after the last drive. A hot engine makes parts expand and increases the risk of burns. Disconnect the negative battery terminal using a 10mm wrench or socket. Wait five minutes before proceeding. This step is not optional: it cuts power to the engine control unit (ECU) and prevents error codes or accidental short circuits when unplugging the throttle position sensor and electronic throttle actuator.

Work in a well-ventilated area. If you’re in a garage, leave the door open. Gasoline vapors can linger, and throttle body cleaner is flammable. Keep a fire extinguisher nearby as a general workshop precaution.

Removing the Stock Throttle Body

The factory throttle body sits between the air intake tube and the intake manifold, on top of the engine toward the driver’s side. Access is straightforward on the FR-S — no need to remove the intake manifold, though you may want to unclip the intake tube for better clearance.

Step 1: Loosen the intake tube clamps

Use a Phillips or flathead screwdriver to loosen the two clamps securing the rubber intake tube to the throttle body and the air filter box. Slide the tube off the throttle body and set it aside. You don’t have to remove the entire intake assembly, but freeing the tube gives you room to work.

Step 2: Disconnect the electrical connectors

The throttle body has two connectors: the throttle position sensor (TPS) and the throttle actuator motor. Use a small pick to depress the locking tab on each, then pull gently to separate. Avoid yanking by the wires. Label the connectors with a piece of tape if you’re worried about mixing them up — though they are keyed differently and only fit one way on the Trick Flow unit.

Step 3: Remove vacuum hoses

You’ll find a few vacuum hoses connected to the stock throttle body. Typically there is one larger hose (PCV or breather) and possibly a smaller one. Use pliers to squeeze the clamp ears and slide the hose off. Note the routing — take a smartphone photo for reference.

Step 4: Unbolt the throttle body

Using a 12mm socket, remove the four bolts that fasten the throttle body to the intake manifold. The bolts are captive (they stay in the throttle body) on the stock unit, but they may fall out on the Trick Flow unit, so keep them organized. Once all bolts are loose, wiggle the throttle body gently to break the gasket seal. Lift it straight off and set it on a clean workbench.

Step 5: Clean the intake manifold surface

With a rag and throttle body cleaner, thoroughly clean the mating surface on the intake manifold. Remove all traces of the old gasket material and any carbon deposits. A clean surface ensures a perfect seal. Do not let any debris fall into the intake ports — stuff a clean rag into the manifold opening while you work.

Preparing the Trick Flow Throttle Body

Inspect the new throttle body out of the box. Trick Flow machines these from billet aluminum and then anodizes them for durability. Check for any burrs or foreign material inside the bore. If you see anything, gently wipe with a lint-free cloth and a small amount of cleaner. Do not use abrasives.

Transfer any necessary hardware from the stock unit to the Trick Flow body. The stock throttle body may have a small rubber cap or a metal bracket that needs to be reused. Compare the two side by side. The Trick Flow unit typically has the same bolt pattern but a larger bore — note the smooth transition into the intake manifold. Install the new gasket provided by Trick Flow onto the intake manifold studs or alignment pins (some years use dowels). Make sure the gasket is oriented correctly — it only fits one way.

If you wish, apply a very light smear of dielectric grease to the inside of the electrical connectors to prevent moisture ingress.

Installing the Trick Flow Throttle Body

Step 1: Position and bolt

Carefully set the Trick Flow throttle body onto the intake manifold, aligning the bolt holes with the gasket. Hand-start all four bolts. Do not use power tools — torque them by hand using a torque wrench set to 7 ft-lbs (84 in-lbs). Over-tightening can crack the composite intake manifold or warp the throttle body. The spec is low; a firm snug is all you need. Torque in a cross pattern to ensure even compression.

Step 2: Reconnect electrical connectors

Plug in the throttle position sensor and actuator connectors. You should hear a distinct click. Route the wires away from any moving parts or hot surfaces. Use zip ties if necessary to secure the harness.

Step 3: Reattach vacuum hoses

Slide each vacuum hose back onto its corresponding nipple. Ensure the clamps are positioned over the barb and tighten snugly. A small leak here will cause a rough idle.

Step 4: Reinstall the intake tube

Slide the rubber intake tube back over the throttle body inlet and tighten both clamps. Make sure the tube seats fully — the lip should be even all around. If your FR-S has a cold air intake, you may need to adjust the tube length to fit smoothly.

Step 5: Double-check everything

Revisit each bolt, connector, and clamp. Wiggle the throttle body to confirm it is secure. Turn the throttle plate by hand (with the engine off) to feel that it opens and closes smoothly without binding.

Post-Installation Steps and Idle Relearn

Reconnect the negative battery terminal. Tighten to 10 ft-lbs. Turn the ignition key to the ON position (do not start). Wait 10 seconds. Turn the key OFF. This allows the ECU to power up and recognize the new throttle body. Now start the engine.

The first start may be a bit rough — the ECU needs to relearn the idle position, especially with a larger throttle body. Let the engine idle for five minutes without touching the accelerator. If the idle is unstable, blip the throttle to 2000-2500 RPM a few times, then let it return to idle. Drive the car gently for the first 10 miles to allow the ECU to adapt. After a few key cycles, the idle should settle to normal.

Some owners report that a scan tool or an idle relearn procedure using a Techstream cable is helpful for a faster reset. You can also disconnect the battery again for 10 minutes, then perform the same key-on/key-off sequence. If the idle remains high or surging, check for vacuum leaks at the gasket or hoses.

Performance Gains and Tuning Considerations

The Trick Flow throttle body’s larger bore reduces restriction at high RPM, allowing more air to enter the combustion chambers. Sensors like the mass airflow (MAF) and manifold absolute pressure (MAP) will adjust fuel trims within limits, which is why you gain 10+ horsepower without a tune on a stock engine. However, an ECU tune (E85 or 93 octane) can extract even more power by optimizing ignition timing and fuel for the increased airflow. Tuning also smoothes out any tip-in throttle response oddities that sometimes occur when you change the bore size.

For reference, installers have measured gains of 10-14 hp on a normally aspirated FA20 with the Trick Flow unit alone, and up to 18 hp when combined with a good intake and header. Check out forums like FT86 Club for real-world dyno charts and owner experiences.

If you plan to track the car or want every bit of response, consider pairing the throttle body with a lightweight pulley or a cold air intake. But even alone, the Trick Flow throttle body transforms the way the engine breathes above 4000 RPM. The FA20’s notorious torque dip (around 3500-4500 RPM) is slightly mitigated, though a header/tune combo is the true fix for that. Still, the throttle body is a cost-effective, reversible mod that makes the FR-S feel snappier in daily driving.

Potential Issues and Tips

  • Check engine light (CEL): A P0121 or P2138 code can appear if the throttle body connector is not fully seated or if the throttle plate is sticking. Recheck connections and ensure the plate moves freely. A quick ECU reset usually clears it.
  • Idle surge after install: This is normal for the first few restarts. If it persists, perform a full idle relearn procedure (disconnect battery for 10 min, then key-on 20 sec, key-off 10 sec, start).
  • Loss of low-end torque: Some drivers notice a slight lag off idle because the larger bore reduces intake velocity at very low RPM. The tradeoff is worth it for top-end power. If you drive mostly around town, the stock throttle body may suffice, but the Trick Flow still delivers a more responsive pedal feel after adaptation.
  • Gasket leaks: Use a quality gasket and do not reuse the old one. Listen for a whistling sound at idle. A vacuum leak can cause lean AFR and rough running.

Final Thoughts

Installing a Trick Flow throttle body is a Saturday afternoon project that rewards you with measurable horsepower and a sharper throttle. The process is straightforward even for a novice mechanic, as long as you take your time with the connectors and torque specs. Whether you’re building a naturally aspirated powerhouse or simply want to revitalize your stock FR-S, this upgrade is a proven stepping stone. For those hungry for more, Trick Flow also offers intake manifolds and cylinder heads for the FA20, but the throttle body alone gives you an excellent taste of what careful airflow engineering can do.

For additional reading, check out this Trick Flow throttle body product page for technical specs and installation notes. You can also explore the Scion FR-S official website for service manuals that complement this guide. And remember: a brief test drive after completion is the best way to confirm a job well done. Enjoy the extra 10+ horsepower and that newfound eagerness as you press the pedal — your FR-S will thank you.