One of my 240's has the re-occuring check engine code 123 problem. Changed out the sensor with a new Bosch but it still occurs. A month ago I cleaned all the ground connections and problem seemed to go away for a awhile but now its back again. I've seen a number of similiar post and a couple of different ideas to the cause. Has found the actual problem? Was thinking of changing to a new 87C thermostat and possibly adding some redline water wetter.