Three things. First, make sure the sensor has a solid 12V between the RED and BLK wires. If not, that power circuit runs from the ECM reference supply through the M72:F102 SMJ connector, make sure something hasn't got the SMJ wet. Second, the push-latch connectors used in that period were very vulnerable to water intrusion if they got beat up a bit. The sensors are pulled-up 3-wire Halls, so it only takes a small amount of corrosion to trash the CKP signal. Get a flashlight and magnifier and check the female connector pins, corroded ones will generally appear off-color and not shiny. Lastly, any Hall will be sensitive to bad grounding, so backprobe the BLK wire and do a voltage drop test to the chassis (not the engine block) with the engine idling. Anything more than about 40mV indicates undue resistance in the ground path. If it's high, to see if that's the issue, use the backprobe for an external ground jumper to the body and see if the sensor's disposition improves. Note that the ground path also runs back into the car through M72:F102, that's why you check to the body and not the block. So it's possible your whole issue is a crummy gang-ground underneath the dash.