Afr's randomly drop 3 points while driving
 

I have a 91 turbo miata running ms2 and innovate mtx-l and recently the car will randomly drop 3 points on afr gauge and stay there for a while around like 11.1 cruising. Sometimes the car will be normal, 14.7 cruise and 12 under boost. Almost like the car has two different modes? I changed the wideband sensor thinking it went bad and it changed nothing only other thing I can think of is the wideband itself or maybe a wiring issue with wideband itself. Car ran great before this and any help greatly appreciated - Brady

Tune and log please

Tune and log like Curly said, AND check the vacuum line going through the firewall into the MS.

DO NOT assume it is OK just by looking at the thing.
Start the car and wiggle the vacuum line while keeping an eye on the AFR / Vacuum gauge.

If you do not have those gauges, hook up your laptop. TS will have them on your screen.

Also, pull up your VE table and look at it in 3D mode to make sure you don't have unintended peaks and valleys.
Some laptops have very sensitive touch pads and that has the potential to create unpleasant surprises on tables and whatnot.

Check your grounds and power connections. Resistance changes can do funny things.

If you have a vtps your EA settings could be out of whack too

Ill try to post log tomorrow, in middle of moving so no internet but heres info on car, no vtps https://www.miataturbo.net/build-thr...-thread-93517/

No vtps?

That's not good.

Its been running fine for the past two years?

They usually don't excel enrich very well and bog instantaneously when you move the throttle quickly.

Found the source of the problem, coolant temp is directly related with the wack afr readings, dumps fuel when it reads low assuming the coolant sensor is clapped, pretty sure ms2 uses the one on the thermostat neck? Think ive heard there is also a coolant sensor in the rear.

No the one on the thermostat neck is for the 1.6 fan. The single wire on the back of the head is for the gauge cluster, and the 2 wire with a green plug is the ECU sensor. Randomly dropping out like that, I’d expect a bad wiring connection, not a bad sensor.

Going to change it out anyways, wiring looks good from a glance and if sensor doesnt fix it ill look into wiring further

**fixed**
Was the coolant sensor; thanks to whoever suggested logging it, forgot that was a thing lol.