Octavia 2.0TSI Temp Gauge showing overheating but not overheating! And terrible cold start.

[TeebsVRS]

Had an issue with my 64plate 2.0TSI VRS today, had driven about 25 miles then parked up for over an hour. When leaving the car park I noticed my cooling fans were blowing, checked the coolant gauge and it was wobbling erratically up and down between 90 and 130 degrees. 

 

Pulled over, no sign of overheating but called Skoda Assist/AA anyway. With ignition on but engine not running it was still wobbling about above 90 at random. AA fella confirmed the engine was cool, unplugged the two coolant sensors he could see but the gauge was still erratic so said it's most likely a wiring or other sensor fault. On the way home with him following me the gauge maxed out at 130 and the overheating warning came up and fans on full, but drive normally. After a 45min drive home in quite heavy slow traffic the engine and rad were pretty cool.

 

2 weeks ago I had my waterpump/stat and timing chain replaced after a leak was diagnosed to the thermostat, with a note that a multiplug appeared to have had coolant leaking on it and may be damaged. The garage confirmed they had checked it over and cleaned it out and it seemed ok.

 

Doubt it is related, but I had also accidentally ran the car without the oil filler cap for a short 4-5 mile journey and ever since it has had a terrible cold start, with the revs dropping and stalling and a very rough lumpy running for about 10-20 secs after which it seems to find the correct smooth idle, especially if you give some revs to help it. The garage recently replaced two magnet solenoids which they said seemed stiff and were recommended to be changed by a VW master tech , but it's still exactly the same.

 

Anyone had anything similar to any of these issues, and had a successful fix?

[TeebsVRS]

In case this helps anyone searching for issues, the coolant temp sensor tucked away on the head seems to have been the cause of this. Coolant had leaked here and damaged wiring - a new sensor has fixed the cold start issues completely.