MacBook Pro i5 running at only 800mhz.

[drewwils]

Extreme lag on a used 2011 MacBook Pro I bought for my parents. Intel Power Gadget shows CPU is running at 800mhz with no fluctuation. Zero. Booted into diagnostics and no problems were found. Can't return it.

Any ideas?

 

[Schranke]

what is the temperatures when the machine is running?
Since this is presumedly newly bought, is it a clean install?
What is the battery status?

 

[drewwils]

what is the temperatures when the machine is running?
Since this is presumedly newly bought, is it a clean install?
What is the battery status?

Clean El Capitan install on a new SSD. No battery - only used as a desktop. Strange, temperature is ~64°C (149F) on Amazon Prime Video ~50% load and streaming Xfinity (Flash) using ~85% load and extreme lag.

 

[iMacC2D]

Clean El Capitan install on a new SSD. No battery - only used as a desktop. Strange, temperature is 64°C (149F) on Amazon Prime Video ~50% load and streaming Xfinity (Flash) using ~85% load and extreme lag.

That's the problem. The machine throttles the CPU back significantly with no battery installed.

 

[Schranke]

That's the problem. The machine throttles the CPU back significantly with no battery installed.

Yep, the battery acts as a power reserve to provide burst energy when needed (not often) the machine will throttle to prevent draining more than can be provided by the adapter.
I once stumbled upon a thread which talked about how to modify this feature.
Here are a links to get you started (This is at your own risk, personally I would just get a new battery)
https://apple.stackexchange.com/que...step-when-using-macbook-pro-without-a-battery
Edit: a few more links
https://arstechnica.com/civis/viewtopic.php?f=19&t=1392381
https://www.insanelymac.com/forum/topic/306819-disable-speedstep-on-a-late-2011-mbp-with-yosemite/

 

[drewwils]

Well, I just replaced the battery and it's still at a flat 800mhz.

 

[elathus]

Has to be an original battery I think, otherwise it will keep throttling. Lost a couple of days over this just a week ago, before figuring it out.

 

[Schranke]

Has to be an original battery I think, otherwise it will keep throttling. Lost a couple of days over this just a week ago, before figuring it out.

What do you mean by original battery?
I changed one I my moms Mac with a replacement from ifixit, that is not an original battery, but I did not see any limitation on performance.

 

[elathus]

I believe ifixit sells OEMs, which are basically originals, not so cheap replacements from ebay/aliexpress. But it seems like it differs from mac to mac. 2010 mbp at work works just fine without battery. Mine 2015 throttled.

 

[Count Blah]

I have used "non-original" batteries, and have had it work. Check 'Power' or 'Battery' under 'About this Mac' and tell us what it says for battery health information.

 

[elathus]

If it's not the battery, if it's not overheating, then it's probably one of the sensors on the motherboard. I got lucky the problem being just the battery.