Finding the 3mm socket head screw can be tough, and over time it fills with gunk. Try coating a 2.5mm allen wrench with WD40 and inserting it into the socket to help clean it out. Then see if the 3 will fit. Do all that with the engine off. In fact you can make adjustments with the engine off, and then fire it back up again.
However you mention that the engine is rough when cold and warm, and that means it probably isn't the sensor height. When warm yes, but cold the mixture goes very rich, outside the adjusters range.
If it were me, I'd pull the injectors and get the pump turning, and lift the sensor plate and check the injector spray patterns - just fire them over the cam cover. They should all produce a nice even cone of fuel, and make a whistling sound. When the plate drops back, they should shut off cleanly, no drips. All should begin flowing fuel at the same instant as well.
If that check is passed, you're on to something else.
Rhys