Most likely he has a leak in the evaporator core which is almost impossible to detect with dye. A freon sniffer near the vents will confirm this. Unfortunately, it is a huge job to replace it and insure the system is sealed properly.
That sensor is part of the distributor. You can drive but the PCM will not be able to change ignition timing for optimal performance. Replace the distributor.
Have you tightened the spark plugs enough. Is the gap correct. Are the wires put on correctly (all the way on). Are the wires mixed up. Have you cracked any of the plugs (sometimes hard to tell)