Help diagnose me!
My NB Miata has a rough idle when cold. When it warms up it is about 20 degrees cooler than usual (194-198 degrees f). Once it is up to temperature (the lower temperature) the idle is fine. When I drive it in a spirited manner the temp will go up to normal but it will return to the cooler temp after a few minutes.
The gauge itself reads about the same as it always does, my temperature figures are based on a device that hooks to the obd port that displays temperature.
I changed the thermostat a few months back, so that can possibly but not nessisaraly be ruled out. My thoughts are the coolant temp sensor is misreading the temperature and telling the ecu to send in more fuel therefore cooler temp.
Anyone have any ideas, am I on the right track? Also, the symptoms coincided with a air filter change. Probably just a coincidence but could increased airflow have anything to do with it?
RedGT
Dork
8/9/17 9:34 a.m.
So the low temp readings AND the rough running both coincide with the air filter change? I would say it's entirely possible the MAF or the coolant temp sensor wiring were somehow bumped/damaged/something during that install.
My first thought was the coolant temp sensor.
Temperature sensors can be tested with an ohm meter. All you need is a chart for reference.
Bench test temp sensor, if not bench test MAF
I started with cleaning the maf sensor since it was the easiest to do and I have had limited free time. I totally forgot to keep an eye on the temp gauge on the way to work. Although it is a short drive and in cooler morning temps it is less likely to get to full operating temp. Will actually pay attention after work when I will take it for a good drive. Idle seems better though.
A follow up in case anyone else runs into this.
The solution was the Intake Air Temperature Sensor. After doing some further digging I decided to change it. The problem was solved. Curiously there was no CEL for this, perhaps because the ECU didn't think anything was up.
