I have a 91 Golf 1.8 liter. While investigating my rough idle problem I checked the coolant temperature sensor. Something's amiss. The sensor is in the block located directly below the second spark plug from the left. It has two wires and a shield. The jacket is brittle and missing in many places as it had been laying up against the block. The electrical shield is in tact and seems no worse for wear. I measured it various time and it always reads zero ohms. I checked for continuity between the shield and the pin so I know I was reading the correct pins. I had alligator clips and wiggled them around to eat through any corrosion that may have been on the pins. I was using a digital Fluke multimeter. The sensor is therefore bad I say. But wait! The temperature gauge on the dash is working. So I slip a 1,000 ohm resistor in place of the sensor to see if the idle or gauge is effected. Nothing. The engine was pretty much warm during this whole operation. What gives?
Do I not have the coolant temperature sensor? There is another sensor in the head on the right side of the engine just above the output to the heater core. Could that be the coolant temperature and I am looking at the block temperature?