I have a mk 3 Octavia RS upto date with its services (160 000 kms). It’s just started having a low idle issue on cold starts. The revs drop too low and it stalls. After even a minute of driving it’s fine. I’ve also noticed that the analogue temp gauge shows that it’s pretty much at temperature on a cold start (~80 degrees) but the digital oil temperature gauge seems to be working correctly. Could this be a thermostat issue? I’m guessing that the ecu thinks the engine is hotter than it is and isn’t delivering a rich air fuel mixture as it should for a cold start.

4 hours ago, Chichalundo said:

I have a mk 3 Octavia RS upto date with its services (160 000 kms). It’s just started having a low idle issue on cold starts. The revs drop too low and it stalls. After even a minute of driving it’s fine. I’ve also noticed that the analogue temp gauge shows that it’s pretty much at temperature on a cold start (~80 degrees) but the digital oil temperature gauge seems to be working correctly. Could this be a thermostat issue? I’m guessing that the ecu thinks the engine is hotter than it is and isn’t delivering a rich air fuel mixture as it should for a cold start.

More likely the engine CTS is reading high, and therefore leaning off the cold start enrichment more than it should.

I would suspect a faulty engine coolant temperature sensor. 
 

if it thinks the car is warm when it’s actually cold = less fuel = stall