Last year my MX-5 NC struggled to pass its emissions test.
5 years ago I replaced the front cat exhaust manifold with a 4-1 non-cat manifold, moving the oxygen sensors around the remaining mid pipe cat. The mechanic after some diagnostics felt the car was running too cold and recommended changing the thermostat. I did notice the temp gauge dropping when driving fast in high gear with low revs.
I’ve changed the thermostat, but the gauge looked low still, so I hooked up a ODB2 reader and the car is running at 85 deg C. Is this still too low? Can the temperature sensor give a low reading and thus still overfuel due to the ECU thinking that the engine is too cool? Any thoughts or guidance?