P0307 on 2006-2010 Audi S8 5.2L V10: Cylinder 7 Misfire Causes and Fixes

What's Unique About the 2006-2010 Audi S8

The 2006-2010 (D3 generation) Audi S8 uses a 5.2L V10 FSI engine (engine code: BSM), a design derived from the Lamborghini V10. While ignition coil failure is common on most Audi models, this specific engine is notoriously prone to severe carbon buildup on the intake valves. This buildup occurs because the Fuel Stratified Injection (FSI) system injects fuel directly into the cylinder, so gasoline and its detergents never wash over the intake valves. Oil vapors from the crankcase ventilation system then bake onto the hot valves, forming hard deposits that restrict airflow and cause misfires. This issue is so prevalent that it should be considered a primary suspect after basic ignition components are checked, a common misdiagnosis trap.

Symptoms You May Notice

• Flashing or solid Check Engine Light
• Rough or vibrating idle
• Engine hesitation or stumbling during acceleration
• Noticeable loss of power
• Reduced fuel economy
• Smell of unburned fuel from the exhaust
• Difficulty starting, especially on cold mornings

Most Likely Causes

1. Ignition Coil Failure 🔴 High Probability → Shop Ignition Coil Ignition coils are a common failure point on many Volkswagen and Audi engines, including the 5.2L V10. They operate under high heat and electrical load, and simply wear out over time. The original coils are often red.
   How to confirm: Swap the ignition coil from cylinder 7 with another cylinder (e.g., cylinder 6). Clear the codes with a scanner and drive the vehicle. If the code changes to P0306 (misfire on cylinder 6), the ignition coil is faulty.
   Typical fix: Replace the faulty ignition coil. It is highly recommended to replace all 10 coils and spark plugs at the same time to ensure reliability and prevent future misfires.
   Est. part cost: $30-$60 per coil
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug
   How to confirm: After ruling out the ignition coil, swap the spark plug from cylinder 7 with another cylinder. If the misfire code follows the spark plug, the plug is bad. Visually inspect the plug for wear, oil fouling, or damage to the electrode or ceramic insulator.
   Typical fix: Replace the faulty spark plug. It is best practice to replace all 10 spark plugs as a set. NGK is a common OEM supplier for this engine.
   Est. part cost: $15-$25 per plug
3. Carbon Buildup on Intake Valves 🟡 Medium Probability The 5.2L V10 uses Fuel Stratified Injection (FSI), where fuel is injected directly into the cylinder. This means fuel never washes over the intake valves, allowing oil vapor and combustion byproducts to bake onto them, forming hard carbon deposits. This is a well-documented issue for this engine and its platform mates, often requiring cleaning every 40,000-60,000 miles.
   How to confirm: This requires a visual inspection using a borescope inserted into the intake ports with the intake manifold removed. The presence of thick, black carbon deposits on the valves confirms the issue.
   Typical fix: The intake manifold must be removed, and the carbon deposits must be physically cleaned from the intake ports and valves. The most effective method is walnut shell blasting, though some shops use a multi-step process with chemical soaks and manual scrubbing. This is a labor-intensive job, typically 8-10 hours.
   Est. part cost: $50-$100 for gaskets and seals
4. Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector Direct injectors operate under very high pressure and can become clogged or fail electronically over time. Symptoms can be identical to carbon buildup, making diagnosis tricky. A leaking injector can cause a strong fuel smell or even fuel to dilute the engine oil, which is a critical issue.
   How to confirm: This is more difficult to diagnose. After ignition and carbon issues are ruled out, a mechanic can perform specific tests to check injector flow rates and spray patterns. Swapping injectors is not a simple task on this engine as it requires intake manifold removal and special tools for the Teflon seals.
   Typical fix: Replace the faulty fuel injector. Due to the labor involved, some owners elect to replace all 5 injectors on the affected bank at the same time. The new injector must be coded to the ECU.
   Est. part cost: $100-$200 per injector

Rare But Worth Checking

• Vacuum Leak: A leak in a vacuum hose or intake manifold gasket can introduce unmetered air, leaning out the mixture for one or more cylinders and causing a misfire. A smoke test is the most effective way to find a leak.
• Low Fuel Pressure: A failing fuel pump or clogged filter can cause low system pressure, leading to lean conditions and misfires, though this often affects multiple cylinders (P0300).
• Low Compression: A mechanical engine issue, such as a worn piston ring, leaking valve, failed valve stem seal, or head gasket failure, can cause a loss of compression in cylinder 7, preventing proper combustion. A compression test followed by a leak-down test can confirm this. In rare cases, a rocker arm can become dislodged.

Diagnosis Steps

1. Read the fault codes with an OBD-II scanner (like VCDS for VW/Audi) to confirm P0307 and check for any other related codes. Note the freeze frame data for RPM, load, and temperature.
2. If the check engine light is flashing, minimize driving to prevent catalytic converter damage.
3. Locate cylinder 7: on the US driver's side (left bank), it is the second cylinder from the front bumper. The firing order is 1–6–5–10–2–7–3–8–4–9.
4. Swap the ignition coil from cylinder 7 with an adjacent cylinder (e.g., cylinder 8). Clear the codes and drive the car. If the fault code changes to P0308, the ignition coil is the problem.
5. If the misfire remains on cylinder 7, swap the spark plug from cylinder 7 with the one from the cylinder you just used. Clear codes and re-test. If the code follows the plug, it's a bad spark plug.
6. If the misfire still stays on cylinder 7, the issue is not a simple ignition component. Visually inspect for vacuum leaks around the intake manifold and associated hoses. A smoke test is the most definitive method.
7. The next most likely cause is carbon buildup. This requires removing the intake manifold and using a borescope to inspect the intake valves.
8. If carbon buildup is not the issue, investigation should turn to the fuel injector for cylinder 7. This may require professional diagnostics to test flow and spray pattern.
9. As a final step, a compression test and a cylinder leak-down test can be performed to rule out any mechanical engine damage within cylinder 7.

Parts You'll Likely Need

• Ignition Coil (OEM #07K905715F (often red), with many revisions. Verify by VIN.) — This is the most common failure item causing a single-cylinder misfire on Audi engines.
  Trusted brands: Bosch, NGK, Eldor
  OEM price range: $50-$70
  Aftermarket price range: $30-$60
• Spark Plug (OEM #NGK PFR7S8EG or similar. Verify by VIN.) — A standard wear item that is essential for proper ignition. A worn or fouled plug is a frequent cause of misfires.
  Trusted brands: NGK, Bosch, Denso
  OEM price range: $20-$30
  Aftermarket price range: $15-$25
• Intake Manifold Gaskets (OEM #07L133075A (Upper), 07L129717E (Lower)) — These must be replaced if the intake manifold is removed for carbon cleaning or injector replacement.

Related Codes That Often Appear With This One

• P0300 — If the condition causing the misfire is not isolated to one cylinder (e.g., vacuum leak, low fuel pressure, or widespread carbon buildup), the computer may log P0300 for 'Random/Multiple Cylinder Misfire Detected' along with P0307.
• P0301-P0310 (excluding P0307) — If other cylinder-specific misfire codes are present, it points towards a more systemic issue like carbon buildup, a failing fuel pump, or a major vacuum leak affecting an entire cylinder bank.
• P2006 / P2007 — Intake Manifold Runner Control Stuck Closed. Severe carbon buildup can cause the intake runner flaps to bind or stick, often triggering these codes alongside misfire codes.

Technical Service Bulletins (TSBs) & Recalls

• Audi TSB 01-23-41 (2014753/12): While not specific to the V10, this TSB discusses issues caused by fuel deposits, including misfires (P030x) and rough running. It recommends using a fuel additive (G 001770A2) as a first step for cleaning injectors and combustion chambers. For FSI engines, it notes that manual cleaning is required for intake valve deposits.
• Audi TSB 24-08-13: Relates to an Engine Control Module (ECM) software update. Some owners report that dealers will apply a software update as a first step when a misfire is reported due to carbon, though manual cleaning is often still required.

Platform-Specific Known Issues

• Carbon Buildup: As a direct-injection (FSI) engine, the 5.2L V10 is highly susceptible to carbon deposits on the intake valves, which is a primary cause of misfires, especially on cold starts. This is not a question of 'if' but 'when' this service will be needed.
• Dual ECU and MAF setup: The V10 uses two Engine Control Modules (one for each bank) and two Mass Airflow sensors, which can complicate diagnostics if issues span both banks.
• Intake Manifold Runner Flaps: The complex intake manifold has runner flaps that can get stuck due to carbon buildup, leading to airflow issues and fault codes like P2006/P2007 in addition to misfires.

Mechanic-Grade Diagnostic Values

• Low-Pressure Fuel System (LPFP) — expected: 5.0 to 6.5 Bar at idle, viewable in VCDS.. Failure: Significantly lower pressure may indicate a failing in-tank pump or clogged filter.
• High-Pressure Fuel System (HPFP) — expected: 29 to 32 Bar at idle. VCDS should show 'Actual' pressure closely matching 'Specified' pressure.. Failure: If 'Actual' pressure is stuck at a low value (e.g., 5-6 Bar) while 'Specified' pressure is high (e.g., 25+ Bar), it points to a failed HPFP or a faulty G247 high-pressure sensor.
• Long-Term Fuel Trims (LTFT) — expected: Ideally between -8% and +8%. Values should be checked at idle and steady RPM (e.g., 2500).. Failure: Values exceeding +/-10% indicate a problem the ECU is compensating for. A high positive value (e.g., +25%) indicates a significant vacuum leak, while a high negative value indicates a rich condition.
• Ignition Coil Primary Resistance — expected: Approximately 0.49 - 0.57 Ohms (This is a general value, not specific to the OEM coil).. Failure: A reading outside this range suggests a faulty coil winding.

Hidden / Shadow Codes Worth Checking

• Live Misfire Counters: VCDS allows monitoring of misfire events per cylinder in real-time, even if the count is not high enough to set a permanent P0307 code. This is crucial for diagnosing intermittent issues. (see via Using VCDS or a similar tool, go to Engine -> Measuring Blocks -> Groups 015, 016, and 017. Cylinder 7's counter is in Group 017. For newer UDS controllers, use Advanced Measuring Values and search for 'misfire'.)

Scan Tool Commands That Help

• VCDS (VAG-COM): Intake Manifold Runner - Basic Settings — If P2006/P2007 codes are present with the misfire, run Basic Settings Group 200. This function cycles the intake runner flaps to check for binding/sticking, which is often caused by carbon buildup. The procedure requires holding the brake and full throttle while the test runs.
• VCDS (VAG-COM): Intake Manifold Flap - Output Test — To individually test the function of the intake manifold flap motors (V157 and V183) to see if they are responding to commands from the ECU. This helps isolate a dead motor from a physically stuck flap.
• VCDS (VAG-COM): Fuel Pump Relay Test / Activation — To manually activate the in-tank low-pressure fuel pump. This can be used to verify the pump is functional and to prime the system or, as one user did, to flush debris from the tank through the fuel lines.

Wiring & Ground Locations

• ECU Pin for Cylinder 7 Ignition — The ignition trigger signal for cylinder 7 is sent from Pin 3 of the main ECU connector.. If a coil and plug are known-good but there is still no spark on cylinder 7, a technician can probe this pin to check for a signal. A missing signal points to a wiring break between the ECU and the coil connector or a faulty ECU driver.
• Ignition Coil Connector — The 4-pin connector on the ignition coil for cylinder 7.. This connector provides power, ground, and the trigger signal to the coil. The wiring harness leading to it can become brittle from heat and fail. A 'wiggle test' on this harness while the engine is running can help identify intermittent connections.
• Engine Ground Straps — There is a primary engine-to-chassis ground strap located on the front right side of the engine, near the alternator. Other critical grounds exist, and their failure can cause widespread electrical issues, including misfires.. A corroded or loose ground strap can cause a weak spark across all cylinders, but it can sometimes manifest as a misfire on a single, more sensitive cylinder first. Checking that grounds are clean and tight is a crucial step.

Real Owner Repair Stories

• Ross-Tech Forums User (2007 Audi S8 5.2L V10) — Odd fuel trims, lean codes (P2179), and misfires.
  ❌ Tried (didn't work) Replacing all spark plugs, Swapping ignition coils, Replacing the oil separator, Performing a carbon cleaning
  ✅ What actually fixed it The user's long-term fuel trims were maxed out at +25% after the carbon cleaning, indicating a massive vacuum leak. The strong implication, though not explicitly confirmed with a final fix post, was that the intake manifold gaskets were not sealed correctly during reassembly after the carbon cleaning, causing the persistent lean misfires.
• YouTube - 'Diagnosing Why This Audi S8 Misfires' (Audi S8 (appears to be a V8 model, but diagnostic principle is identical)) — Cylinder 1 misfire code, rough running.
  ❌ Tried (didn't work) Replacing spark plugs, Replacing ignition coils
  ✅ What actually fixed it After basic parts failed to fix the issue, a compression and leak-down test was performed. The diagnosis pointed to an internal mechanical problem, suspected to be a broken valve spring or a dislodged rocker arm on the misfiring cylinder. This prevented the need for an expensive and unnecessary fuel injector replacement.
• AudiWorld Forums User (Audi S8 5.2L V10) — Sudden misfire on 6 cylinders simultaneously (1, 2, 3, 6, 7, 8).
  ❌ Tried (didn't work) Checking all coils and plugs
  ✅ What actually fixed it The shop diagnosed the issue as a damaged secondary ECU. The user reported that the mechanic suspected water damage was the cause of the widespread failure across multiple cylinders controlled by that ECU.

"I Checked Everything" — The Actual Cause

• In a case on the Ross-Tech forums, a user performed a carbon cleaning but was left with severe lean codes (+25% fuel trim) and misfires. While they couldn't locate a leak with standard checks, the data strongly suggested a large, unmetered air leak. The most probable cause was an improperly sealed intake manifold gasket after the carbon cleaning service, a scenario a smoke test might miss if the leak only opens under specific temperature or pressure conditions.

When the Usual Fixes Don't Work

• While P0307 is most commonly an ignition coil or spark plug, do not repeatedly replace these parts if the misfire persists. In one documented case, after new plugs and coils failed to resolve the issue, the root cause was identified as a mechanical failure (a broken valve spring or rocker arm), which was only found via a compression test. The owner nearly spent thousands on unneeded fuel injectors before the correct mechanical diagnosis was made.
• Carbon cleaning is the go-to fix after ignition parts are ruled out. However, the repair itself can introduce new faults. One owner continued to have severe misfires and lean codes after a carbon cleaning service. The evidence pointed to a massive vacuum leak, likely caused by an intake manifold gasket that was damaged or improperly seated during reassembly.

OEM Part Supersession History

• 06F905115F (and earlier variants) → 07K905715F, 07K905715G — Revisions to improve reliability and performance. The red-top coils (often ending in F) were a common upgrade over the original black-top coils.
  Heads up: While many revisions are interchangeable, it is always best practice to replace all 10 coils with the same part number and manufacturer to ensure consistent performance.

Diagnostic Flowchart

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0300 — Random/Multiple Cylinder Misfire Detected. Often appears alongside P0307 when carbon buildup or vacuum leaks affect multiple cylinders across the engine.
• P0306 — Cylinder 6 Misfire Detected. Mentioned in the diagnostic steps as the expected code if a faulty ignition coil is swapped from cylinder 7 to cylinder 6.
• P0308 — Cylinder 8 Misfire Detected. Mentioned in the diagnostic steps as the expected code if a faulty ignition coil is swapped from cylinder 7 to cylinder 8.
• P2006 — Intake Manifold Runner Control Stuck Closed Bank 1. Frequently triggered on the 5.2L V10 when severe carbon buildup causes the complex intake manifold runner flaps to stick.
• P2007 — Intake Manifold Runner Control Stuck Closed Bank 2. A companion code to P2006, also caused by carbon buildup jamming the intake manifold runner flaps.

Frequently Asked Questions