Anyone know much about 90s Miata?

11tbantz · Jun 29, 2016

Trying to fix my uncle's car but having no luck. It's a 1990 Maxda Miata mx5 4cyl auto. It will start every time but dies almost immediately, but if I unplug the MAF sensor it will start up and idle fine and I can even bring up the RPMs if I SLOWLY push the gas pedal. If I press it too quickly it just dies. My initial thought was a bad MAF sensor so I put a new one on and absolutely no change. Any ideas or point would be much appreciated.

se7enine · Jun 30, 2016

Unplugging the AFM will allow it to idle but it controls a relay to the fuel pump and it reads air flow and temperature. It could be a bad AFM but you might try this. Open it up and see if it has any bad connections.
http://www.rivercityroad.com/garage/afm_fix.htm

AFM101 : Inside the Air Flow Meter

Connector View
An airflow meter is used on on the 1990-1993 miata. It has three functions, all which are determined by electrical sensors.

1. Airflow On/Off
If the engine is running, it is sucking air. The AFM will close a switch when this happens. Two contacts are used for the switch. The switch is closed to keep the fuel pump running.

2. Airflow Rate
As the air flows thru the AFM, it moves a flapper.The position of the flapper is converted to a voltage (about 3.3 volts at idle). when the engine pciks up speed, it sucks more air, the flapper moves, and the voltage on this pin drops.

3. Air temperature
A sensor inside the AFM changes resistance with air temperature. This determines the voltage on this pin. It goes down as the air gets warmer.

Top View of the AFM.
Electrical View of the AFM

This shows the circuitry inside of the AFM, and its electrical equivalent.

Front View showing the air flapper closed and partially open

The little peg in front of the swing door is the thermister casing.
I'm neither a certifed auto mechanic nor a trained Mazda technician. The information on this page is my own interpretation and may be flat-ass wrong. Use at your own discretion and risk.