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Steady state road tuning on FA20DIT

Road Tuning

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Discussion and questions related to the course Road Tuning

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Hello all,

I'm wanting to get the process started for tuning my '15 WRX myself.

I want to start by calibrating my MAF sensor, however I'm running into issues with steady-state tuning using left foot braking. The car won't allow me to apply braking pressure and throttle at the same time.

Is there any way to circumvent this issue, or can I perform ramp runs with different throttle positions to the same avail?

Thank you,


Hi Christopher, what tuning method are you using? I tuned a FA20DIT WRX using Cobb and didn't have that issue but annoying little limits like this aren't uncommon on newer vehicles. I'd start by seeing if you can disable this feature. in some cases it may be sufficient to just disable TC, however sometimes the flashing software will give you access to maps that limit the torque or throttle opening when the brake pedal is active. Maxing these tables should do the trick. Alternative options include temporarily disconnecting the brake switch at the pedal although I don't recommend doing this unless you're tuning on a closed road - This will almost certainly impact your emergency braking capability so proceed at your own risk. An alternative is to simply gather as much data as you can by using different gears to allow more/less TPS input at specific rpms. This, coupled with some hand smoothing should be sufficient to get a good result.

In this case it's a USA mandated safety feature modern vehicles have to avoid unintended acceleration, after the Toyota debacle. Engine output must be reduced if sufficient brake effort is applied for a certain duration. It cannot be disabled by turning off traction control or pulling the ABS fuse.

You can left foot brake briefly and softly before throttle closes, but alternatives include using a higher gear to achieve more load at a given RPM, or driving up hill.

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