Custom mode drops CPU to 400 MHz on LOQ 15IRX9 (BD PROCHOT from the EC, not heat)

[Alphagit8055]

Version

2.34.0.0

OS

Windows 11 25H2 Build 26200.8973

Device Series

LOQ Series

Exact Model

15IRX9

BIOS version

NECN53WW

How to reproduce the bug?

1. Open Lenovo Legion Toolkit and select custom mode.
2. Keep any fan curve, including the stock custom curve.
3. Launch a game (reproduced in Red Dead Redemption 2) or any heavy CPU load.
4. Watch the CPU clock in ThrottleStop or HWiNFO.
5. Observe repeated drops to 400 MHz with recovery between drops.

Expected Behavior

Custom mode holds clocks like performance mode, with only the fan curve differing.

Logs

log_2026_08_09_11_52_45.txt

Additional information / Video

Custom mode is the only way to set a custom fan curve, and the only mode with this bug. While custom mode is active, the CPU clock repeatedly falls from about 4000 MHz to 400 MHz under load. Performance mode and the other presets hold the clock normally on the same machine, same game, same day.

Frequent 400 MHz drops. In RDR2 the frame rate falls to about 20 FPS during each drop. Switching to performance mode stops the drops immediately.

Evidence, ThrottleStop 9.7
Temps at the drop: 78-84°C, far below the throttle point. Heat is not the trigger.
PKG power clamped to 35.2 W at capture, 53.7 W session max. Performance mode pushes 80 W+ on this CPU.
Limits line shows BD PROCHOT active (red BD PRO, PROCHOT 100°C). The signal comes from the embedded controller.
The BD PROCHOT toggle in ThrottleStop is grayed out on this platform, so no software mask exists.

Already checked
Performance mode versus custom mode on the same load: only custom mode drops.
Latest BIOS installed. Lenovo ships no separate EC firmware download for this model, and the BIOS package carries the bundled EC version.
Multiple fan curves tested in custom mode. The drops appear with all of them.
ThrottleStop EPP and performance checkboxes: no effect. The BD PROCHOT toggle is locked on this platform.

Guess for the maintainer
Custom mode writes CPU power and temperature limits to the EC over WMI. On the 15IRX9 firmware, the written values, or the periodic re-write itself, make the EC assert BD PROCHOT and drop the CPU to the 400 MHz floor. Performance mode never writes those limits, which explains the clean behavior there. Please verify the limit values and units custom mode sends for this model, or skip the power limit writes on models where the EC rejects them, and keep fan curve control working.

Offer
Happy to provide ThrottleStop logs, HWiNFO logs, or toolkit traces on request.

[XKaguya]

Performance mode never writes those limits

Because it was pre-defined preset in BIOS.

Please verify the limit values and units custom mode sends for this model, or skip the power limit writes on models where the EC rejects them, and keep fan curve control working.

This is exactly how LLT works if you don't modify Advanced values in Custom Mode.

It should be EC's issue instead of LLT. Unless official does not.
But recently, Some user found that Temperature Limit will cause specific issue, like frequency drops.

As for your problem, LLT uses exactly same API as what Lenovo Official uses. So i can't say much based on current information.

[Alphagit8055]

• Copied every performance preset value into custom mode: CPULongTermPowerLimit 85, CPUShortTermPowerLimit 162, CPUCrossLoadingPowerLimit 45, CPUPL1Tau 56, CPUTemperatureLimit 97, GPUPowerBoost 25, GPUConfigurableTGP 80, GPUTemperatureLimit 87, GPUTotalProcessingPowerTargetOnAcOffsetFromBaseline 45, GPUToCPUDynamicBoost 0. The 400 MHz drops continue unchanged.

• Tested with the stock fan table, no custom curve. Drops continue.

• Temperature limit changes change nothing, so the temperature limit is not the trigger on this firmware.

The custom profile now carries values identical to the performance preset, and the issue still reproduces. So the trigger is not the values. The remaining difference between the modes is the write path: performance mode switches a BIOS preset with no per-limit writes, while custom mode writes each limit and the fan table over WMI. ThrottleStop shows BD PROCHOT asserted during each drop at temps around 80 C, so the EC fires the clamp after the GodMode writes.

One more data point: this same laptop on the same BIOS ran fine on the older discontinued release 2.26.1. The regression arrived with a newer release.
Questions:

What changed in the GodMode apply path between [old version] and the current one: write order, added writes, the Fan Full Speed check, the fan table FSTM write?

Would you add a per-write skip toggle (power limits, fan table) to let affected users bisect the offending WMI call?

[XKaguya]

Copied every performance preset value into custom mode: CPULongTermPowerLimit 85, CPUShortTermPowerLimit 162, CPUCrossLoadingPowerLimit 45, CPUPL1Tau 56, CPUTemperatureLimit 97, GPUPowerBoost 25, GPUConfigurableTGP 80, GPUTemperatureLimit 87, GPUTotalProcessingPowerTargetOnAcOffsetFromBaseline 45, GPUToCPUDynamicBoost 0. The 400 MHz drops continue unchanged.

Copy value doesn't change the Mode based issue. EC runs different in different power modes.

The only thing GodMode apply changed is the custom fan table. If you can make sure that even newest action have this issue.

Currently i have no idea why and how this happened.