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.

[emerydc8]

I had the exact same problem on my 94 E420. I thought it was the ETA, so I replaced it and still got the problem, intermittently. I lived with it by shifting to neutral at stops so the engine would settle down.

A few days after replacing the ETA, I replaced the Neutral Safety Switch, but since the problem was intermittent, I honestly can't remember if the problem eventually went away by itself before replacing the NSS or if the NSS actually solved the problem. In any case, I know for sure that I haven't had the issue since replacing the NSS.

If you are thinking about throwing parts at the problem, I would consider replacing the NSS first. I did have a similar problem with my 400E (surged in reverse only) and the NSS did solve that problem.

[Gilly]

May need to be reset or "relearned", try turning the key to ON with the engine not running and waiting a minute or so, it will usually just relearn it's position all by itself, if not it might need to have a shop computer to a relearn on it. If it relearning by itself you will faintly hear the throttle motor running itself from closed to open and back again.