[TurboQ89]

I'm getting this code for "Thermostat for mapped engine cooling (F265), short to ground", and the resultant (?) codes P2187 and P2189 for "system too lean at idle". Also get P0507 for "idle control system higher than expected". The car seems to run well, now with 91k miles.

I know this 2008 V8 is a different engine than the early cars, and I can't find anything written on P0599. Also don't know where F265 is. Maybe my thermostat or temp sensor is bad, but is there really a wire on a thermostat ? Anyone have any ideas for me before I am forced to take it to the dealer?

 

[FSJ Guy]

Do you have VCDS? That will tell you what your temp sender is telling the ECM.

If the ECM is getting the wrong coolant temp, the fuel mixture could end up being wrong.

That also explains the idle speed error. If the ECM thinks the coolant is cold, it will enrich the fuel mixture AND bump up the idle speed to warm up the engine faster. Conversely, if it thinks it is already warmed up, the idle speed will be too low (for the actual temp) and the mixture will not be rich enough for decent idle when cold.

That is, IF the coolant temp sender really is bad.