engine temp sensor spec
 

G'Day guys, i am chasing a rough idle whem the engine is warm on my 300TE M103 1989MY. I just measured the engine temperature sender after getting home (40 min drive) with the engine off. I measured from each terminal post to earth and got around 260 ohms and steadilly declining. I measured it again with the engine running ant it wat about 370ohm and declining at a rate of amout an ohm/sec.Is this normal? I haven't measured it cold and will do in the morning but my idle issue seems to come into play as the engine warms.

The resistance of a Bosch coolant temp sensor for the fuel system has been the same since the late 60"s.

With the engine cold (approx 70F) the value should be around 2500 ohms.
And on a HOT engine between 250-350 ohms.

Never seen a coolant temp sensor cause idle issues on a M103 engine

ditto,might be valve stem seals allowing the engine to burn a little oil when cold.

**UPDATE** Tested the temp sensor and it was within spec. I also changed the 02 sensor and it has reduced the roughness of my idle by 80-90%, it is now starting to feel like a MB! The remaining idle rumble is pretty much identical in frequency to the original rumble prior to swapping out the 02 sensor much much, much less significant. I am guessing it was over fuelling and now i need to chase the final reminants of the rumble but for the moment i am very satisfied.