Moeye

I don't have a service manual, I figure somebody on here can help me out. I have a code 31 that comes on when the throttle is fully closed. It idles fine. The previous owner installed a SAFC on the car. I check the Karman sensor reading. It's reading 3 Hz when the engine is not running. And it reads only 3 Hz from 600 rpm to 1500 rpm (no load, tranny in park)... as soon as it breaks over 1500 rpm, the reading jumps between 3 Hz and 46 Hz. If I rev a little more then the reading is much more stable.

What can be causing the mis-readings at rpm below 1500 rpm? I changed out the Karman Vortex sensor twice already, the symptom still remains.

Durrr

is the honeycomb damaged at all?

could also be a weak ground on the sensor connector. clean it with electrical contact cleaner.