My 89 Turbo Wagon and I've been experiencing some jumpy idle at start, and then the check engine light has come on. The light dissappears after the car is shut off. I checked and it's a Code 21. So I bought a coolant temp sensor and am wondering if anyone has any experience installing one of these. Thanks y'all!

Use pipe thread tape for the sensor below the thermostat.  Use nothing for the one in the radiator.  Use nothing for the one in the top of the engine.

I did just that! Thanks!!