10K POTENTIOMETER INSTALLATION INSTRUCTIONS:

1. Disconnect the car’s negative battery cable.
2. Remove the driver’s side access panel from the center console.
3. Locate the terminal number 85 wire coming out of the ECU. Normally, a 2G electrical shop manual is required to determine where to find terminal number 85. I’ll try to describe the location as best as I can here: There are 4 plastic connecting plugs which have between 12 and 24 terminals each plugged into the ECU. Looking up at the ECU from under the steering column with your left ear pointing toward the floor of the car, you’ll see that there are two rows of terminals, an upper row (closest to the engine) and a lower row (closest to the radio). Terminal 85 is located in the lower row, on the fourth plug from the left; it’s the fourth pin starting from the left edge of the fourth plug. If you’re looking at the ECU and can’t find it, you need an electrical shop manual.
4. Cut the terminal number 85 wire and install a 10K potentiometer in the circuit as shown above. Use enough wire so that the potentiometer can be mounted on the dash somewhere convenient and within reach.
5. Make sure that the two connections are adequately electrically insulated.
6. Replace the access panel.
7. Reconnect the negative battery cable.
8. Start up the engine and measure air-fuel ratio while driving the car. Air fuel ratio should be set around 12.5 to 13.2 whenever the turbo is making boost above 5 psi. 12.5 is more conservative. Never let the air-fuel ratio go higher than 14.7 when at boost. If it does, immediately get off the gas and adjust it down.
9. Do not attempt to adjust idle and off-idle air fuel ratios. The ECU is in a closed loop mode at low rpm and low boost. It will override your circuit modification back to a factory set idle air-fuel ratio. Not adjustable in closed loop.