Hello all, I am experiencing a problem with my D that has me puzzled. I started it up for the first time in 5 months and it started with no problem at all. as the engine sat idling for a few minutes until it reached operating temperature it ran like a champ. As soon as it gets to normal operating temperature the idle starts to fluctuate between 7000 and 10000 RPMS. As it fluctuates I can hear the Frequency valve slowing down almost stopping at times (this is where the engine starts to drop in RPM) then the Frequency valve will jump "alive" again returning to normal (where the engine will idle normally). This is a continuous cycle of the engine going up and down in RPM's and every time I hear the frequency valve dying out then returning to normal again. Now my questions: 1. Could there be something wrong in my Lambda circuit causing this such as a bad O2 sensor? 2. Could my frequency valve be bad? Either part is expensive so I don't want to "swap it out to see if it fixes it" and later find out it wasn't it at all. I am assuming that if the Frequency valve would be bad it would just not work which leads me to believe that there may be a problem with my O2 sensor? Does this sound logical? My CPR valve works like a charm. When it's cold and I start the engine it will start off at like 1-1.5 Bar and slowly work it's way up to 3-3.5 bar as the engine warms up. My fuel pump, Accum and fuel filter are all new as are the fuel lines. I know it can't be my Fuel distrib (or could it?) since the engine runs fine until it warms up to operating temperature. Any suggestions? Thanks in advance. Steve