location of coolant temp sensor

[mac townsend]

1984 (3/84) 325E 5-speed, with air & cruise control (not working, but that's not for now). 220,000 miles when odo quit (don't know when that was--I just got the car as a theft recovery)

Trying to resolve a won't meet Calif smog issue.

I will be putting in a new O2 sensor and then a new "generic" cat---the full monte thing (downpipe and all the way to the flange at the back) is simply out of my budget range for this project.

I'm watching the idle speed vary and thinking it could be the temperature sensor...so I tried to check the resistance per Bentley/Per Bosch Fuel Injection & Engine Management.

There are two sensors on the t'stat housing on this car. One uses a "bosch clip" like on the injectors and the other uses plain spade connections (two leads, both brown IIRC, bad lighting may have hidden a stripe color on one).

One of these is the termo-time switch (controls the cold start valve) and the other is the coolant temperature sensor

but how can I tell which is which?

(interesting to see that 46 folks have looked at the message but none suspects the answer.)