Manually opening an EGR valve with a vacuum pump or scan tool will cause the engine to idle roughly or stall.

Question

Quizplus · Accepted Answer

Manually opening the EGR (Exhaust Gas Recirculation) valve introduces exhaust gases into the intake manifold, which can disrupt the air-fuel mixture balance, leading to rough idling or stalling, especially if the engine is at idle or low load conditions where it's not designed to handle large amounts of EGR flow.

Manually Opening an EGR Valve with a Vacuum Pump or Scan