Hi folks,
I have mentioned this previously and have spoken to the dealer - the dealer was no help - insisted there was no problem, and the tech did not know what normal actually was... So here I am again!

Background: I have a 2012 MCS manual with 13000 Miles, and an EcoRoute HD module with a Garmin GPS. The car is otherwise stock in the engine compartment and related areas... I use the GPS primarily as a set of gauges to monitor coolant temp, battery voltage, intake temp, and boost. Timing advance is there too, but more for interest than any function for me. I recently had the car in for the coolant temp sensor replacement per the recall.

I have 2 related but (I suspect) different failures.

1.
Since very new the car has stumbled a bit at idle when cold. With coolant temps around 40-60C, when the engine slows to idle, it stumbles a couple times then settles. On a couple occasions, the car has failed to start, though this hasn't re-occurred in the last 8 months. After the coolant temp sensor replacement I did note a change on the Garmin - coolant temps never indicated below 25-30C even when the car sat out overnight at well below 0C. It now does indicate ambient temps (close to, anyways) at start up after a cold soak, but the stumble is still there.

BMW says all is normal... Can anyone report on how normal 'my' stumble is?

2.

This summer we had one day that got super hot - +35C (I know only 35C - we like it colder up here! ) or hotter, and up until then I had always seen the same behaviour from the coolant temp on the Garmin: It would rapidly warm up to 102C and stay glued there unless I stomped on the gas - it would then plummet to 96C, stay there until I relaxed my foot, at which point it would race back up to 102C. I think I saw 103 or 104C twice up 'till the fateful day, and below 96C only while warming up.
On that day, as I drove my usual highway route to work in open traffic, AC going, at the halfway point of my 20km drive, the coolant temp was still not at 102C but around 78C, and not climbing at all. Usually by then, I am at full temp, and my fun ramp from 1 highway to the other would induce the drop to 96C (what I was looking for) rather than seeing a low temp to begin with! It took until a km or so from work for the temp to GET to 102C (cycling the AC had no effect... ...on the engine - I roasted), and since then, it has fluctuated lazily - slowly moving up to 102 on warm up, generally holding the temp from 99-104C during steady driving, and dropping to less than 80C if I get aggressive with the throttle. I have seen 109C a couple times in stop and go traffic this summer.
Can anyone comment on the behaviour of their coolant temp - is it VERY steady at 102C with the expected drop to a lower value when driving spiritedly, or is my lazy thermostat normal? When I took a tech with me in the car to show him, he first off didn't know if the coolant temp indication on the Garmin was actually coolant temp (he suggested it might be some sort of calculated value or other mumbo jumbo), or how the engine was supposed to behave in any event! He did not know what 'normal' was.

Your help is appreciated!
Eric