Why Upgrade to a Siemens 70mm Throttle Body?

Upgrading your vehicle’s throttle body is one of the most straightforward ways to improve airflow into the engine, which directly translates to better throttle response and increased horsepower. The Siemens 70mm throttle body is a popular choice among enthusiasts because it offers a significant bore size increase over many stock units (typically 60–65mm), without requiring major modifications to the intake manifold or engine management system. By allowing more air to enter the combustion chamber during each cycle, the engine can produce more power, especially when paired with other bolt-on modifications like a cold air intake or performance exhaust.

This guide provides a comprehensive, step-by-step process for installing a Siemens 70mm throttle body on a compatible vehicle. Whether you’re a seasoned DIYer or a first-time modifier, following these instructions will help you achieve a clean, successful installation and unlock the performance potential of your car.

Tools and Materials Needed

Before you begin, gather all required components and tools. Having everything on hand will prevent delays and ensure you can work through the installation without interruptions.

  • Siemens 70mm throttle body (ensure it matches your vehicle’s specific part number)
  • New intake manifold gasket (compatible with the 70mm bore)
  • Socket set (metric and standard, sized for throttle body bolts)
  • Torque wrench (capable of reading inch-pounds or foot-pounds as required)
  • Flathead screwdriver (for prying clips or disconnecting hoses)
  • Phillips screwdriver (for air intake duct clamps)
  • Gasket scraper (plastic or brass to avoid damaging surfaces)
  • Clean rags or shop towels
  • Throttle body cleaner or brake cleaner
  • Safety glasses and gloves
  • RTV silicone gasket maker (if the new gasket is not pre-formed or if required by your engine)

Preparation Steps

Proper preparation is critical to avoid damaging components or causing electrical faults. Take the time to set up your workspace and vehicle correctly.

  • Park the vehicle on a flat, level surface and engage the parking brake. Allow the engine to cool completely — a hot engine can cause burns and make removal more difficult.
  • Disconnect the battery (negative terminal first) to eliminate any risk of short circuits or unintended electrical activation when unplugging the throttle body connector.
  • Clear the area around the throttle body of any debris, tools, or loose items. A clean workspace reduces the chance of losing small parts or contaminating the intake system.
  • Review your vehicle’s service manual for specific torque values and any unique procedures related to your make and model. Torque specifications vary widely; using the correct figure prevents stripped threads or leaks.

Removing the Old Throttle Body

With the preparation complete, you can begin carefully removing the stock throttle body. Work methodically to ensure no damage to surrounding components.

  • Locate the throttle body on the intake manifold — it is positioned between the air cleaner housing and the intake plenum, with a large rubber or plastic duct connecting it to the air filter.
  • Remove the air intake ducting: Loosen the clamps on the intake tube using a Phillips screwdriver or socket. Gently pull the duct off the throttle body and set it aside.
  • Disconnect the throttle cable or electronic throttle connector: For older cable-operated systems, unclip the throttle cable from the lever on the throttle body. For drive-by-wire systems, simply unplug the electrical connector by pressing the locking tab and pulling straight out.
  • Disconnect any vacuum hoses that may be attached to the stock throttle body. Note their positions (take a photo) so you can reconnect them correctly.
  • Remove the mounting bolts securing the throttle body to the intake manifold. Use a socket and ratchet; if bolts are tight, apply penetrating oil and allow it to soak for a few minutes.
  • Lift the old throttle body off carefully, being aware of any remaining hoses or wiring. Place it on a clean rag.
  • Clean the intake manifold mating surface: Use a gasket scraper to remove all traces of the old gasket material. Be gentle to avoid gouging the aluminum surface. Wipe the area with a clean rag dampened with throttle body cleaner or brake cleaner to remove any oil or debris.

Inspecting the Old Throttle Body

Before discarding the stock unit, examine it for signs of wear or carbon buildup. This can help diagnose any pre-existing issues such as idle instability or poor throttle response. Heavy carbon deposits around the throttle plate indicate a need for periodic cleaning — a practice that should continue with the new Siemens unit.

Installing the Siemens 70mm Throttle Body

This is the most critical phase. Proper alignment and torque are essential for a leak-free installation.

  • Install the new gasket onto the intake manifold. If the gasket is not self-adhesive, apply a thin bead of RTV silicone to the manifold surface in the locations specified by the manufacturer. Allow the RTV to set slightly before mounting the throttle body.
  • Position the Siemens throttle body over the gasket, aligning the bolt holes and any locating dowels. Do not force it — the throttle body should sit flush without binding.
  • Install the mounting bolts hand-tight initially, then tighten them in a crisscross pattern using a torque wrench to the manufacturer’s specification. Typical torque values range between 90–120 inch-pounds (10–14 Nm), but always verify for your specific application.
  • Reconnect the throttle cable or electrical connector: For cable systems, ensure the cable is properly seated and has appropriate free play (usually 1–2 mm). For electronic throttles, push the connector until it clicks securely.
  • Reattach any vacuum hoses you removed, ensuring they are pushed fully onto the nipples. Replace any cracked or brittle hoses with new ones of the correct diameter.
  • Reinstall the intake air ducting, tightening clamps evenly to avoid distorting the tube. Ensure the duct is not kinked or interfering with other components.

Throttle Body Calibration (If Required)

Some vehicles, especially those with drive-by-wire systems, may require a throttle calibration after replacement. The process varies by manufacturer, but a common method involves turning the ignition to the ON position (without starting the engine) for 10 seconds, then turning it OFF for 10 seconds, and repeating twice. Consult your vehicle’s service manual for the exact recalibration procedure. Skipping this step can result in poor idle, reduced throttle response, or a check engine light.

Final Steps and Test Drive

After installation, a systematic check ensures everything is secure and functioning correctly.

  • Double-check all connections: Inspect the throttle body bolts, intake duct clamps, electrical connectors, and vacuum hoses. Look for any signs of looseness or improper seating.
  • Reconnect the battery (negative terminal last).
  • Start the engine and let it idle for 2–3 minutes. During this time, listen for any hissing sounds (indicating a vacuum leak) and watch for consistent idle speed. If the idle is rough, check for gasket misalignment or loose bolts.
  • Inspect for leaks: Spray a small amount of carburetor cleaner around the throttle body gasket area while the engine is idling. If the RPM increases, there is a vacuum leak that needs to be addressed by tightening the bolts or replacing the gasket.
  • Take the vehicle for a test drive: Start gently, then gradually apply full throttle. Notice the improved throttle response and any new found power. If you experience hesitation or surging, return and verify all connections. Some vehicles may need a short learning period for the ECU to adapt to the increased airflow — 10–20 miles of mixed driving is normal.

Troubleshooting Common Issues

Even with careful installation, issues can arise. Here are the most frequent problems and how to resolve them.

  • Check engine light (CEL) after installation: This often indicates an air leak or an electrical issue. Use an OBD-II scanner to read the code. Common codes include P0101 (Mass Air Flow sensor range/performance), P0505 (Idle control system), or P0120 (Throttle position sensor). Address the cause rather than just clearing the code.
  • Vacuum leak: A high idle (above 900 RPM) or a hissing sound points to a leak. Re-torque the throttle body bolts in a crisscross pattern. If that doesn’t work, remove the throttle body, inspect the gasket for damage, and reinstall with a new gasket or additional RTV.
  • Idle stuck high or surging: This can happen if the throttle plate is not closing fully. Check for interference between the intake duct and the throttle lever, or verify that the throttle return spring is functioning. For electronic throttles, recalibrate as described earlier.
  • Poor throttle response: Ensure the throttle cable (if applicable) has proper adjustment. Too much slack reduces response; too little prevents the throttle plate from closing fully. For drive-by-wire, scan for codes and perform a recalibration.
  • No performance improvement: The Siemens 70mm throttle body works best when the engine can take advantage of the extra airflow. If your vehicle is otherwise stock, the gains may be modest. Consider pairing the throttle body with a cold air intake, performance exhaust, and a tune to fully realize the benefits.

Performance Tuning After Installation

To maximize the horsepower and torque gains from your new throttle body, consider these complementary modifications and adjustments.

  • ECU Tuning: A custom or off-the-shelf tune can adjust air-fuel ratios, ignition timing, and throttle mapping to suit the larger bore. Many tuners offer specific calibrations for the Siemens 70mm throttle body. Without a tune, the factory ECU may gradually adapt, but peak gains often remain locked behind the original software.
  • Cold Air Intake: Replacing the restrictive factory air box with a high-flow intake ensures the throttle body receives enough clean, cool air. A free-flowing intake is almost a prerequisite for a 70mm throttle body upgrade.
  • Port Matching: If you are comfortable with minor porting work, matching the intake manifold opening to the 70mm bore can eliminate a step change in airflow. This requires careful attention to keep a smooth transition.

Maintenance Tips for Your Siemens Throttle Body

A quality throttle body like the Siemens unit should provide years of service with minimal maintenance. However, periodic cleaning and inspection are recommended.

  • Clean every 30,000–50,000 miles or whenever you notice a rough idle or hesitation. Use a dedicated throttle body cleaner (never use carburetor cleaner, which can damage the throttle position sensor or coatings).
  • Remove the intake duct and spray cleaner onto a clean rag, then wipe the throttle bore and plate. Do not spray cleaner directly into the engine; it can foul the MAF sensor or cause a hydraulic lock.
  • Check the gasket condition at each cleaning. Replace if it appears brittle or compressed.
  • Inspect the throttle plate seal: When the plate is closed, there should be minimal light visible around the edges. Excessive gap can cause idle issues and vacuum leaks.

Conclusion

Installing a Siemens 70mm throttle body is a rewarding upgrade that can sharpen throttle response and unlock extra horsepower, especially when combined with supporting modifications. By following this detailed guide and attending to torque specs, gasket sealing, and post-installation checks, you can complete the job with confidence. Remember to allow the ECU time to adapt, and consider a professional tune to fully exploit the larger bore. With proper installation and maintenance, your Siemens throttle body will deliver reliable performance for many miles.

For further reading, consult the official Siemens product page for technical specifications, and check enthusiast forums like PerformanceForums.com for vehicle-specific tips and tuning advice. Always cross-reference torque values with your vehicle’s factory service manual for the best results.