Throttle cut

Definition

Throttle cut is any condition which causes the ECU to reduce the throttle pedal angle, even if the actual accelerator pedal potentiometer is at WOT.

The two main causes of throttle cut are

ESP activity (a.k.a. traction control)

The ECU senses that one or more wheels are losing traction. It does this if ESP is enabled and the ABS wheel sensors show a large discrepancy in wheel speeds.

Boost deviation

Actual boost pressure exceeds desired boost pressure by around 200-230mbar (3-3.3 psi). The ECU will only restore throttle angle once actual boost pressure falls to at or below the desired boost pressure.

Examples

Throttlecut.csv shows a 3rd gear run where the ECU cuts throttle.

Notice the throttle plate angle drops suddenly from 100% to 43%-48% when the deviation goes over ~200mbar.

Throttle cut onset

TIME	RPM	Throttle Plate Angle	Boost Pressure Desired	Boost Pressure Actual	Deviation
497575	4025.75	99.6078431372549	2327.109375	2490.625
497645	4046.75	100	2315.1953125	2508.90625	193.7	.9228	1.084
497716	4114	100	2302.1484375	2503.0859375	200.9	.9201	1.087
497786	4151.5	99.6078431372549	2271.1328125	2508.2421875	237.1	.9055	1.104
497856	4200.5	45.8823529411765	2263.1640625	2488.203125	225.0	.9100	1.099
497926	4230	43.921568627451	2248.3984375	2457.65625

Notice the throttle does not return to 100 until the boost pressure actual returns to almost exactly the boost pressure desired.

Throttle cut recovery

TIME	RPM	Throttle PlateAngle	Boost Pressure Desired	Boost Pressure Actual	Deviation
499748	5183	48.2352941176471	2200.546875	2222.8515625
499819	5211	48.2352941176471	2208.0078125	2226.5625	18.6
499889	5246.5	48.2352941176471	2216.2109375	2217.34375	1.1
499959	5294.5	77.6470588235294	2220.234375	2194.8046875	-25.4
500029	5319	100	2227.1875	2166.2109375

Getting rid of throttle cut

• Use Lemmiwinks to cut SEL Scaling. However, this also reduces maximum horsepower, so it is not the optimal solution. Also, in some cases it can exacerbate throttle cut, since the requested boost is now lower. If the actual boost remains just as high, there is a higher chance of deviation induced throttle cut.

• Add back pressure to slow the ramp. If you are using open dumps or test pipes, try using a more restrictive exhaust system.

• Use the "3/4" throttle mod (putting a stopper below the accelerator pedal), which prevents the driver from pushing the throttle to 100%. This, however, can also reduce overall power.

• Use a master boost controller in parallel to set a hard limit on the actual boost.

• Use a throttle cut defender to "trick" the ECU into thinking the actual boost is lower than it is.

• Adjust the Motronic ME7.1 boost maps to prevent initial boost spikes. Alternately, the maps can be adjusted such that the requested boost is always at or above 200mbar below the hard MAP limit. In the latter case, it is strongly recommended that an MBC in parallel be used to prevent overboosting, since the ECU can not know how far above MAP limit the manifold pressure is.