I think you're looking in all the wrong places and I'm not even sure you have all those sensors and things on a 103 motor. If you've already changed the OVP relay, my money is on a dodgy solder in the ICU or a flaky wire.
First thing you should do is check to see if you have power going to the ICV when the engine is idling at 500 rpm. If no power, you need to trace it back to the OVP and from there to the ICU to find the short. What worked for me was giving the ICU a good whack which would restore power and idle control.
Another thing I can recommend is the purple wire grounding idle mod. You'll need to search for more info on this but its good for raising the idle another 50rpm which will help a lot with stalling issues if you have got something dodgy in the idle control. I'll see if I can find my notes or the links but IIRC the procedure is different between the 190 and 300E so you'll need to do some research yourself. It does work, though. I can vouch for that.