2006-2010 BMW M5 & M6 Intake Manifold: The Gateway to Throttle Actuator Failure

Understanding the S85 Intake Plenum

On the 5.0L V10 engine (known as the S85) in the 2006-2010 BMW M5 and M6, the intake manifold is more accurately called an air collector or plenum. Unlike V-engines with separate manifolds for each cylinder bank, the S85 uses one large plenum that covers the entire top of the engine. This plenum feeds air to ten individual throttle bodies, a design borrowed from motorsport that gives the M5 and M6 their incredible throttle response. Because of its large size and central location, the plenum must be removed to perform many common services, including spark plug changes and, most importantly, throttle actuator replacement.

Symptoms of a Failing Intake Plenum

While the plastic plenum itself is fairly durable, it can develop problems over time, primarily vacuum leaks from cracks in the housing or failed gaskets. A vacuum leak allows unmetered air to enter the engine, bypassing the mass airflow sensors and disrupting the air-fuel ratio. Symptoms of a vacuum leak include:

• Rough or Unstable Idle: The engine may struggle to maintain a steady RPM at a stop, sometimes surging or feeling like it's about to stall.
• Hissing or Whistling Noises: You may hear an audible sucking or hissing sound from the engine bay, which is the sound of air being pulled through a crack or bad gasket.
• Check Engine Light: A vacuum leak will often trigger a Check Engine Light with lean condition codes, such as P0171 (System Too Lean Bank 1) and P0174 (System Too Lean Bank 2).
• Reduced Power and Poor Acceleration: The incorrect air-fuel mixture can cause hesitation and a general loss of performance.

The Real Issue: Throttle Actuators and Other Related Parts

More often than not, the intake plenum is removed not because it has failed, but to access other components underneath it that have. The most notorious of these are the throttle body actuators.

Throttle Body Actuator Failure

The S85 engine has two throttle actuators, one for each bank of five cylinders. These electronic motors control the throttle butterflies. They are a well-known, extremely common failure point due to the original plastic gears inside wearing out. When an actuator fails, the car will immediately go into "limp mode," drastically reducing engine power.

Symptoms of throttle actuator failure are distinct from a vacuum leak and include:

• Sudden loss of power and the engine entering "limp mode".
• DSC and EML warning lights illuminated on the dashboard.
• Specific fault codes such as 2B15 (Throttle Valve Actuator Bank 1) and 2B16 (Throttle Valve Actuator Bank 2). Other related codes include 2B21 and 2B22.

Diagnosing Intake System Problems

To confirm a vacuum leak from the intake plenum, the most effective method is a smoke test. A technician will force low-pressure smoke into the intake system with the engine off. If there is a leak in the plenum or any of its gaskets, smoke will be seen escaping from the source of the leak. This is a much more reliable method than spraying flammable liquids like brake cleaner or propane around a running engine.

Buying a Used Intake Plenum for Your BMW V10

If your intake plenum is cracked or damaged, a quality used OEM part is an excellent alternative to an expensive new one. The original BMW part is well-made, and a used one can provide years of reliable service if inspected properly. Here’s what to check:

• Inspect for Cracks: Carefully examine the entire plastic housing, paying close attention to the mounting points and the seams where the two halves of the plenum are joined. Heat and vibration can cause hairline cracks to form.
• Check All Mounting Tabs: Ensure all plastic tabs and bolt holes are intact and free of damage. Broken tabs can prevent the plenum from sealing correctly, leading to vacuum leaks.
• Verify Flatness: Place the plenum's mating surfaces on a known flat surface to check for any warping, which could compromise the gasket seal.
• Look for Heat Damage: Any signs of melting or severe discoloration could indicate the part came from a car that experienced an engine fire or extreme overheating event. Avoid these parts.
• Plan on New Gaskets: Never reuse old intake plenum gaskets. Always purchase a new set of gaskets to ensure a proper, leak-free seal during installation.

Replacement Cost Comparison

The cost of replacing the intake plenum is dominated by the price of the part itself and the labor to access it. Since throttle actuators are often replaced at the same time, their cost is included for a realistic estimate.

Intake Plenum Replacement Overview

Replacing the intake plenum on the S85 engine is an involved process best suited for experienced DIY mechanics or a professional technician. The difficulty is rated as 4 out of 5.

The general steps involve removing the front strut braces, disconnecting the airboxes and mass air flow sensors, unplugging numerous electrical connectors and vacuum hoses, and carefully unbolting the ten clamps that secure the plenum to the throttle bodies. Accessing the rear clamps can be particularly challenging. Once the plenum is lifted off, you gain access to the throttle actuators, idle air control valve, and spark plugs.

Frequently Asked Questions (FAQ)

OEM Part Numbers and Specifications

The primary part discussed in this guide is the main upper intake plenum, also called the air collector.

• OEM Part Number: 11617834458
• Alternate Part Number: 7834458
• Material: Plastic