Hi peeps
since I bought my a3 it had starting and running issues which I eventually tracked down to a split breather pipe allowing un metered air in through said split and into the engine through the inlet manifold link .
now all has been great with it starting on the button every time however on Sunday needed a bit of cranking to get going has has been the same since on every COLD start up !
I have scanned it and got

" 16500/P0116/000278 - Engine Coolant Temp. Sensor (G62): Implausible Signal

Possible Symptoms
Starting the engine when engine is warmish or warm, idle rpm immediately is 1200 - 3000 rpm.
Diesel: an indication is extreme long time burning time of the glow indication light.
With all engine temperatures seldom idle rpm will vary between 900 - 1000 rpm.
With engine warm (90 °C) the engine temperature suddenly drops (70 °C) and slowly comes back to 90 °C."

however as part of my initial problem solving I did fit a new "blue square 4 pin " coolant temp sensor !
Where do I go from here ? And also could this problem also be causing my 1600 rpm idle ?
as always any help is greatly appreciated