1995 e420 idle oscillating

[paschov]

My 1995 E420 started to have erratic idle, surging, misfire, etc. I pulled fault code 4 from fuel injection module and replaced MAF sensor with a used one. Now I have a steady idle, but ONLY with A/C on. With A/C off it's continuously fluctuating between approx. 400 and 600 RPM, no surging, no stalling, just steady fluctuation. It doesn't fluctuating in Parking or Neutral, no matter of A/C status. The engine wiring is OK, was already replaced. Throttle motor was also replaced last year with a rebuilt one. Other engine controlling modules such as E-GAS and ignition, return no fault codes. What's the problem? Thanks in advance.