Is my ECU faulty?

Technical Area Electrics & ICE
41

I’ve known MAF sensors to fail on similar age cars. If you can get a known good one for decent money maybe worth substituting it to eliminate it if nothing else. They’re hard to diagnose reliably I find.

42

Shinobi,

I know that this isnt your main problem, but in your original post you mention the battery voltage. I monitor the voltage of my Miata battery constantly from the 12v socket. 11.5v is low for the battery itself, but if you are in luck may just indicate it needs charging properly. 14.2v or so when the alternator starts charging is good, but indicates a high rate of charging. You may probably need to drive for an hour to get to full charge, at which point the voltage reading will have fallen back to just over 13v. If you cannot achieve this, the battery itself needs testing.

David

43

Hi David,

Thanks for your advice, since creating this post I have replaced the battery with a new one :slight_smile:
It didnt fix any issues but I’m glad its healthy at least

Cheers,
Dan

44

FML. Further down the rabbit hole I go…
Using the process of elimination I continue to diagnose and fix any of the issues relating to the idle droop and rich air/fuel ratio.

Since my last update I have installed a new MAP sensor and re-plugged the vacuum hose on the intake manifold as it should have always been. The previous codes disappeared and were replaced by Oxygen sensor fault codes.

I cleaned the oxygen sensors. No luck.

The car failed its MOT. Turns out it had a de-cat installed. I had no idea :upside_down_face:
I installed a 400 cell sports cat and new oxygen sensors but the poor idle persists.

Oxygen sensor codes have now been replaced with ‘P0037 - Heater Control Circuit Low Bank 1 Sensor 2’

This code specificly relates to the heater element inside the rear oxygen sensor. First I used a multimeter to check the resistance from sensor heater element, which was a healthy 14.8. I then checked that the sensor plug received battery voltage when the ignition was on, which it does. Next I tried to diagnose a faulty return wire to the PCM but unfortunately that appaears to be functioning perfectly too.

I know that my PCM is healthy as I have recently sent it off for examination and no faults were found (Thanks Rob :+1:).

If anybody has any suggestions on how to sort this out I would really appreciated it!