Which action helps stabilize idle RPM during a TSI smog test?

• A. Increase idle by revving engine manually.
• B. Activate the A/C to load the engine slightly.
• C. Turn off the A/C to reduce load.
• D. Remove the air filter.

Answer: (B)

A steady idle during a smog test comes from adding a small, controlled load to the engine so the idle control system has to work to hold the target speed. Turning on the A/C engages the compressor, which places a predictable extra load on the engine. The engine’s control system then adjusts fuel and air to keep the idle RPM at the specified level, resulting in a more stable reading for the test.

That’s why activating the A/C to load the engine slightly is the best choice. It creates a realistic, constant demand that helps prevent idle fluctuation that could occur with no load or with excessive manual revving. Turning off the A/C removes that load, increasing the chance of unstable idle. Removing the air filter would alter air flow and fuel mixture in an unpredictable way, which isn’t appropriate for a controlled test environment.