300TE-24V sometimes low idle, low voltage at ICV

[kevinnathanael]

Hi all, I have a 1990 Mercedes 300TE-24V with the following symptoms: low idle when in gear and AC turned on (when turning on AC after the rpm goes a bit down, it does not go back up at all). I tried measuring voltage at the Idle Control Valve (ICV) and its showing around 1.8v. I tried a M103 car and it measured 11-12v. I have tried switching over the OVP, ICV, Jetronic module, but voltage stayed at 1.8v.

However when I try to start the car the following day, everything is normal and voltage is at 11v. This idle drop happens ocassionally, and so when it does I have to wait till the following day until it gets normal.

Any suggestions on where else to look?

 

[DREAMER NO2]

The valve is connected to a spring and the control voltage is applying a torque to turn the valve against the spring. The relationship between the control voltage and the valve rotation angle is pretty linear, starting from a negative angle to a positive angle with 4 volt as zero degree. Of course, the voltage vs air flow is nonlinear. The torque of a torsional spring is linear w.r.t. its torsional elastic deformation. (T=k theta) The actual engine control must be closed-loop with the air flow measured as a feedback. It is true that if the OVP stops providing voltage (for example, a burned fuse as in the case in another thread) and the control voltage is zero, the air flow is not zero because no torque is applied and the valve resumes its initial equilibrium position at a negative angle. What condition is the OVP relay ?