temperature sensor change.
 

Hi. I just changed the temperature sensor from the old black one to the newer green one, as my temperature guage needle was dropping occasionally. After I changed it, the engine started idling erratically. I have not driven it yet, so I cannot tell how badly the fuel management has been affected. I put the old sensor back in again and the engine continued to run badly. I obtained the sensor from the local motor factors company, who I have known in the past to provide reliable parts.
Is the sensor the cause of the erratic running, or do I need to do anything else to get the engine to idle properly? Should I bleed the coolant system? Should I run the engine for a few minutes to allow the ecu diagnostics to reset? Is there any vagcom technique that I need to know about/use?
If I go to the Audi dealer and buy an Audi/OEM sensor, and fit it, will this cure the erratic idling/engine, or will I need to get a vagcom fuel trim reset performed or similar? Could the ECU have been damaged by the sensor?

Many thanks in advance.

It's not the sensor. No need to bleed the system. Running it longer will not solve the problem. You disturbed something else during the repair, perhaps the sensor wire. Vagcom the codes and Check your work and anything else in the vicinity.

thanks
 

thanks, I'll check the wires, but I wonder if the sensor is dodgy and has damaged the ecu, or put the fuel trims/mixture out of alignment in some way. I'll have to get someone to vag com it. Thanks anyway.

You implied the engine ran fine with a bad sensor
 

Just an erratic display (which could be a bad cluster). Very doubtful a bad sensor would fry an ECU

sensor
 

I didn't think that it could, but I'm wondering why the erratic idling when I returned old sensor. I can check the connector block/wires with a multimeter, but I've read that the sensor can be the cause of the temp gauge fluctuations. I'm picking up a new OEM sensor soon, so hopefully that will correct the issue.

Thanks

Had similar symptoms... changed the temp sensor, but still erratic movements in temp guage. Started to monitor the coolant temp using the climate control display and discovered it was the coolant thermostat going bad.

2001 audi tt quattro
36k miles
original and mint


Cluster temp rarely gets above 70c
When I run the coolant temp through climate display slowly but steadily climbs to 90c (seems to take quite a while) and sticks there. No overheating.
Cabin is warm within 5 mins.

Fuel consumption is very high - just over 10 litres per 100 kilometres of highway travel - supposed to be about 7.7 litres for every 100 kilometres of highway travel.

Any suggestions on sensors or troubleshooting?