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To avoid anyone losing time reading this all, the solution that worked twice is: Restore your PC using "System Restore" to a point in time prior to when you started experiencing this problem

Today I notice that my one year old laptop Lenovo X1 Carbon (Windows 8.1) is 2,5 times slower on everything, only when AC is attached.

As soon as I detach the AC to go on battery, performance magically goes back to normal, and as soon as I plug the AC, performance is immediately slower.

I checked with Task Manager and Process Explorer, no special process sucks my resources (both when AC is attached or not). However my CPU speed decrease significantly in Task Manager > Performance:

enter image description here

I tweak the Power Management Windows configuration with no success, nothing looks abnormal here. Btw, I am always on Maximum Performance plan, both when AC is attached or not.

I investigate the CPU parking stuff with no success, the CPU is not parked, I checked it both with the registry change and with Coderbag CPU core parking manager.

I tweak various BIOS Power options with no success (as explained there answers from CodePrime818 May 2015 at 10:18). They used to have always been set to default and I went back to default after experiments.

Finally I found this related post ThinkPad Windows 7 laptop is often slow but only when plugged into AC power, the answer was:

The real problem turned out to be that I was using a 90W power supply, and the thinkpad's power management mistakenly thinks this is not enough power and slows the CPUs down to save power. Using the 135W power supply fixes it. Some people have other suggestions, even a hardware hack:

I have 2 power suppliers, one bigger one smaller, both produces the issue, I don't know how many W they are here is a photo of the big one. However I haven't changed anything in the power supply, performance uses to be maximum on both, it must somehow comes from a BIOS or Windows setting change?!

enter image description here

Certainly this is related: This weekend the laptop was very low on battery and suddenly ran out of power. A never seen error told me that the clock didn't even have battery and indeed, the next time I restarted the machine it told me the hours with 30 minutes late for like 15 seconds, until it gets the right time automatically (from the network I guess).

I am pretty sure this is related to this issue, but have no idea what alse to do?

Info1: I have Lenovo 2 power suppliers (90W and 65W) both used to make this laptop works fine with AC attached.

Info2: I have a second Lenovo X1 Carbon, exactly same model, that works perfectly with these two power suppliers.

Info3: I just noticed that if I let the AC plugged, then close the screen to provoke sleep mode (not deep sleep mode), and then re-open the screen, push the power-on button, then the laptop is still plugged but now the CPU is back to 2.67 GHz! So at least I'll have a way to work plugged for some time, but I'd really like to fix this once for all.

Info4: Here are the Lenovo software actually installed on this Laptop (I see nothing related to Power Management)

enter image description here

Thanks for your help!

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  • The label says 20V and 4.5A, so it's 90W.
    – David Marshall
    Commented Aug 10, 2015 at 17:38
  • Thanks David, but it used to work fine for more than a year with this power supply, and this cannot be a coincidence this slow down follows this weekend outage incident, is it?
    – Patrick from NDepend team
    Commented Aug 10, 2015 at 17:41
  • Next step in diagnosing: Bust out your multimeter and measure the output of your power supply (the 90W) and ensure it's providing proper voltage and amperage (or simply try another known-good compatible power supply).
    – Ƭᴇcʜιᴇ007
    Commented Aug 10, 2015 at 18:11
  • Does the laptop have Lenovo's 'ThinkPad Power Manager' installed? If so, it may be overriding the Windows power settings.
    – edgerrr
    Commented Aug 10, 2015 at 18:51
  • @TECHIE007 please read the 3 infos I just added, they all suggest that this is not a Power Suplly issue, notr a hardware issue, but a power setting issue.
    – Patrick from NDepend team
    Commented Aug 10, 2015 at 20:44

5 Answers 5

Reset to default
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Note: This is too long for a 'Comment' so I posted it as an 'Answer' even though it's really just some suggestions.

After giving this some more thought, doing a little research, and with the additional information you provided, here are a few things you might try. P.S.-I agree that this is probably not a hardware/AC adapter problem especially given the behavior of "info3" that you provided.

1) I found this at the Lenovo forum titled "X1 Carbon Won't Boot without AC Cord - reset switch" which states:

When servicing the system, or when storing it for an extended period of time, the battery can be electrically disconnected. There is an option in BIOS to disconnect the battery - AC must be unplugged while doing this step.

To start up the next time, attach AC and press the power button.

If the system become hung and will not power down, or will not start even with the AC connected, try using a paper clip to press the small reset button found inside a hole in the bottom of the system.

2) Restore your PC using "System Restore" to a point in time prior to when you started experiencing this problem. You sound very tech savvy so I won't bore you with the details on how to do it.

3) If that doesn't work, you might try doing a "Refresh" of Windows. Microsoft has instructions on how to do this on a Windows 8.1 system titled "How to refresh, reset, or restore your PC". Note: Doing this is pretty drastic since it will remove any apps you've installed from the web (not the Microsoft Store...those will automatically be reinstalled) and from CD/DVD. If the laptop came with Windows 8 installed (has a "Recovery" partition with Windows 8), the laptop will revert to Windows 8 and you will need to manually update it again to Windows 8.1.

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  • Thanks for these suggestions, 2) worked, the problem is solved. I chosed to restore to a point stored on 3rd of August and it now works!! Thanks so much :) I am afraid we will never know the culprit!!
    – Patrick from NDepend team
    Commented Aug 11, 2015 at 8:05
  • It just happened again today and again restoring to a previous point fixed the issue! The cause was, while a saved Windows session took a lot of time to open, I forced the machine to shutdown to restart, and after that the max CPU was locked to 0.78 GHz. And this happened on the twin machine (not the same machine it happened a while back, but exact same model, X1 Carbon with same spec). This is pretty a shame that a pricey Lenovo Thinkpad machine can have such issue :(
    – Patrick from NDepend team
    Commented Mar 12, 2016 at 12:47
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Even though this is a very old thread, this issue still occurs on Lenovo laptops on Windows 10.

A quick 'solution' is to uninstall the ACPI-compliant battery (remove driver as well), and have Windows re-detect the battery. It'll reinstall the driver, but this time it won't throttle the CPU. You don't need to reboot.

Chances are high this will happen again (up to daily) - sometimes it'll be gone for weeks on a row. In any case, this is much faster than having to reset Windows etc.

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My X1 did this as well due to the computer coming out of sleep node while in my backpack for whatever reason. When I got to work the next day I had the sys critical battery shutdown error when I opened it back up when connected to my Thinkpad One Link Pro docking station. It took 10min to come out of that state. I tried restarting and the startup from that took about the same amount of time. I played with the setting in both Windows power options and Lenovo Power Manager to no avail.The processor remained fixed at a max 30% of frequency in the resource monitor.

I was able to fix this issue on my x1 by uninstalling Lenovo Power Manager, and doing a full shutdown (power off). When the computer came back on, the processor was no longer limited.

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  • We have had issues with the Lenovo Power Manager too on several models: X240, X220, T460, Yoga and X1. As it doesn't add anything of value on top of the normal Windows power-management we uninstalled it everywhere. Since then problems are gone. 1 tip: If the battery has, for whatever reason, completely drained, put the laptop on charger for 10 minutes before turning it on again. After it has booted to the login-prompt just reboot it once more to reset the charging logic. This is actually advice for any model/brand of laptop. Not just Lenovo's.
    – Tonny
    Commented Dec 7, 2016 at 16:41
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I had a problem like this on my X1 Carbon where my CPU speed was throttled to a maximum of around 40% whenever it was plugged in. Try going into the BIOS and disabling the option called Intel (R) SpeedStep technology.

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In some cases the problem seems to be caused by a BIOS or hardware issue. In my case, plugging the charger in causes the system (independent of OS) to activate the bd prochot (bi directional processor hot) throttle, as if the GPU were too hot. Deactivating the throttle e.g. via throttlestop (https://www.techpowerup.com/download/techpowerup-throttlestop) solved the problem instantly.

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