Hi there

My 1.9 TDI developed something strange recently. Only on start up after is starts normally the revs would go to 1100 for a short period of time. Outside temperature is around 10. When engine warms up in few minutes it runs normal. The temperature gauge shows around 60-70, only in town around 80. When ‘Test 51-engine coolant temp’ is used on climate control it is showing 90?  Could it be that engine coolant sensor is faulty?

Last year thermostat and temp gauge were changed - temp was showing 90 since. How come that ‘Test 51’ and ECT on display don’t show same temperature? Is the same sensor used for both gauges?
BTW, no error codes on read.