GLC with A/T

Disconnect anti-afterburn valve-to-air cleaner hose at anti-afterburn valve. Start engine and run at idle. Place finger over hose (intake port). Engine speed should not change.

Fig 1: View of Anti-Afterburn Valve Intake port on GLC models differs in design.
Increase engine speed and quickly release accelerator. Suction should be felt at air intake port. If no suction is present or suction lasts for more than 3 seconds, replace anti-afterburn valve.