Are you saying that a faulty engine temperature sensor would cause it to not idle well?
I've now rode about 250 miles and around the time the engine gets hot, the engine idles no problem.
I let it cool down overnight and the next day it forgets where it was idling at.
I'm running out of ideas because I've replaced everything else. O2, Throttle Cables ect
OF COURSE, many items will affect stable idle speed at various engine temperature. On these K1200, the most common failure point being vacuum air leaks - these are subtle and can appear at many point within / around the intake system. It only takes a very small intake leak to have a large effect.
An air intake leak will also make the EFI system behave differently when engine sensor data shows warm compare to cold. Mixture needs are more critical when engine is cold. Thus, an intake air leak will mess-up the EFI computer algo and the combustion process even more when engine is cold. When engine is warm, the symptoms of intake air leak is often a high idle that does not want to go down.
The coolant temp sensor is not the most common item for these issues, but it does have an indirect effect:
When the engine is started, if Motronic EFI sees a cold value from this sensor (higher resistance in 2000 to 3000 OHMS range roughly), it has to assume engine is in fact cold. Hence it does a certain number of things that will in turn affect idle:
- Injectors pulses are longer (create a richer mixture)
- TVA (idle actuator) stepper motor will push on throttle-bodies assy to keep idle speed higher (about 1200 to 1400 rpm for a short period)
If this sensor is defective (or giving bad data) the EFI system is unable to compensate for the mixture need (and idling help) for a cold engine.
IN ADDITION to above:
The internals of the EFI system has a fail safe default mode where it will assume the engine is warm (176 F , 80 Celcius) in case of defect or doubtful data from this sensor. Thus, it is possible to have an engine perform better when warm compare to when engine is cold.
HOWEVER, a defective engine coolant temp sensor is not very common, so I cannot suggest to replace part just to test, Much better to make a series of static tests (engine OFF, ignition OFF) with a multimeter to test resistance at various engine temp (stone cold mean after stopping engine for at least 8 hours). Data values for temp -vs- resistance have been posted earlier.
These simple tests on the Engine Coolant sensor are much easier / faster than searching / troubleshooting intake air leaks. Better start with easier stuff first...
See this photo album for method to test. Keep in mind that on early K1200LT (1999-2001) this sensor connector is located on Left side BUT a bit lower than the photos. Connector has same shape / size as in photos: