A modified 2015 Audi S3 with a Unitronic Stage 2 ECU and DSG tune, along with a catted downpipe and cold air intake, began experiencing misfires around 73,000 miles. Initial troubleshooting included replacing the N80 valve, spark plugs, and coil packs with OEM parts. This temporarily resolved the issue, but the misfires returned. Upgraded RS3 coils and colder RS7 spark plugs were then installed, again providing only temporary relief.
A subsequent diagnostic by a repair shop, without prompting, identified significant carbon buildup. A carbon cleaning service was performed, along with replacement of the injector and intake manifold gaskets, and a preventative water pump replacement due to a minor leak. This resulted in noticeable improvements in idle and acceleration.
However, after approximately 3,000-4,000 miles, the misfires reoccurred. A recent VCDS scan revealed persistent misfire codes and a small EVAP leak code.
Next steps being considered include flashing the car back to its stock tune and performing a smoke test to pinpoint the source of the EVAP leak. Potential causes for the leak, such as the PCV valve, are also being investigated. A reliable and affordable smoke machine recommendation is sought.
Addressing the EVAP leak and ruling out vacuum leaks are crucial steps in resolving the ongoing misfire issue. Given the modifications to the vehicle, returning to the stock tune may help isolate whether the performance enhancements are contributing to the problem. Furthermore, a thorough inspection of the intake system and related components is recommended to ensure proper sealing and function.
While carbon cleaning provided temporary improvement, the recurrence of misfires suggests a deeper underlying issue. Further diagnostics, potentially involving specialized tools like a smoke machine or a pressure tester for the intake system, may be necessary to identify the root cause. Using a VCDS plug to log data related to fuel pressure, boost pressure, and other relevant parameters during driving conditions could offer valuable insights into the cause of the misfires.
A comprehensive approach, addressing both the EVAP leak and potential vacuum leaks, along with careful consideration of the vehicle’s modifications, is essential for a lasting solution to the misfire problem in this 2015 Audi S3. Consulting with experienced Audi technicians or utilizing online forums dedicated to VAG-COM diagnostics may provide further assistance in troubleshooting this complex issue.
