I have a Linde H30D H2X393S06051 with a surging problem. When trying to drive at a steady speed (fast or slow, forward or reverse) the lift will surge as if you are quickly pressing down and letting up on the accelerator pedal. With the laptop computer hooked up I am not seeing any variation coming from the electronics feeding the HPV. I hooked a gauge up to the F port on the filter and I have about 20 Bar of charge oil pressure at idle. When driving the charge pressure fluctuates. It will drop down to about 12 Bar this is when the lift slows down. The pressure will go back up to 20 Bar and the lift will then speed up. Thanks for any suggestions as to why the charge pressure is fluctuating.