How do I adjust fuel flow?

Hi all,

What I am trying to do is adjust the fuel flow in a Learjet 24/25.  The part I want to adjust is the idle fuel flow.  I find the cruise fuel flow to be accurate as far as I can tell. 

I have read that the 20 series Learjets burn about the same amount per hour on the ground as they do at cruise.  From what I have seen the CJ610 idles around 500 pph per engine.  The Learjet I am flying has the aircraft Idling at about 240-250 pph and cruising at about 500-600 pph. 

I want to get the idle fuel flow to read 500 pph with the cruise fuel flow remaining as is. 

I tried adjusting the values in the aircraft.cfg, but they adjust the fuel flow in a linear fashion.  So I can get the engines to idle at 500pph but every other phase of engine RPM is burning too high. 

Can anyone help me to adjust this fuel flow in a non linear way?

Thanks!