George, The frequency valve should be constantly buzzing or adjusting the pressure in the lower chamber of the fuel distributor. It's controlled by the Lambda ECU box which gets it's signal / voltage change from the 02 sensor. Has the 02 sensor been changed lately. That's where I would start. It's very rare that the FV goes out. John Hervey www.specialTauto.com << I have a question regarding the proper operation of the frequency valve. When the engine is warm, is it normal for the valve to stop "buzzing" every 10-15 seconds or should it constantly buzz? Lately I've had an irritating idle surge and noticed the surge is linked to the apparent intermittent operation of the valve. The valve buzzes constantly while the engine is cold/warming up, only when the engine is at operating temp. does this occur. Any suggestions? George #2196 >>