Peugeot 206 1,4i 2003 (8v) CTO (Coolant Temperature Switch)

I have been diagnosing a peugeot 206 with a hard start rough idle  for a very long time now off and on. It has a 1 wire Coolant temperature swittch which is NO and has an opening temperature of 248F (120C) which I have been sturggling to find until I removed the whole engine harness to test and refurbish it.  The switch is spliced in with the signal wire of the Coolant Temp sensor so  assume that when it closes it shorts the temp signal to ground.

Is it possible that if this sensor is stock closed that it would cause the start and idle problem? The car also intermittently refuses to turn the engine cooling fan off when the key is turned off less removing a battery cable and the live data complains about implausible signals for lambda both OS and DS but no codes. It has been kind of a parts cannon project so almost every sensor has been changed that has anything to do with mixture formation, the plugs are new the cat is ned the coil is new the injectors are new and the evap purge valve is new. (Only abs knock Tacho and power steering pressure sensors have not been changed except the temperature switch). I have also changed the fuel pump.

The coolant temp wiring was shorted to ground so there is a good chance the CTS is stuck closed since there was no short with the harness fully unplugged . At the very least I have had the opportunity to refurb and retape the harness.

Thanks.