7M-GE 7M-GTE DP Diaphragm VTV Air Filter DP Diaphragm VTV Air Filter EC-2517 EC-2518 Normal Driving Deceleration VTV DP Diaphragm VTV DP Diaphragm EC3440 EC3439 To reduce HC and Co emissions, when decelerating the dash pot opens the throttle valve slightly more than at idle. This causes the air-fuel mixture to burn completely. Condition Diaphragm VTV Throttle Valve Idling Pushed in by return force of throttle valve CLOSED Idle speed position Normal driving Pushed out by diaphragm spring OPEN High speed position Deceleration Pushed in by return force of throttle valve CLOSED Slightly opens and then slowly closes to idle position