Chosen Solution
I had a huge nightmare when i swapped out the old hard drive for an SSD. I got super excited when everything started working that i forgot to remove the old adhesive from the body and the LCD when i applied the new one. a couple hours later my LCD was on the floor shattered. I reconnected the LCD to the body and i got power and i got an a blank white image. i took it to a repair shop to replace the LCD, which works great, But i noticed that it was Laggy. i did a nova bench mark before the screen fell and my results were cpu 871, gpu558, ram score (24gb) 275, disk- 82 and now they are cpu 63, gpu, 147, ram score(24gb) 211, disk 38 when i got the diagnostic code : PFM006 and my Kernal task fluctuates between 490-1000 % I am going to take it back to see if they are able to repair shop to have them run a couple test to see if it can be easily fixed. what i am afraid of is them recommending me to get the logic board replaced. based on what on this info i am open to hear any opinions on what the issue may be.
You added a tis-bit which could explain things! You stated they replaced the display assemble if they did did they forget to transfer the displays thermal sensor?
Your systems SMC services are kicking in! Basically, it thinks there is something wrong (which likely is) SMC requires constant access to a bunch of sensors for it to work correctly. So we need to figure out which sensor was forgotten or is damaged so the system works correctly. When switching out HDD’s to SSD’s people forget Apple did there own thing within the HDD’s getting custom versions so the systems SMC services can access the drives internal thermal sensor. If someone swapped out your display they likely forgot to transfer the sensor over which you can see here in Step-25 in this guide iMac 27" 2017 Display Replacement In any case even if you where able to slow the fan down via software your systems CPU’s clocking is reduced as part of the protection setup when SMC has lost connection to the sensors. So I really don’t recommend that approach. Think of it this way… Your cars front left wheel fell off, to cheap to get it replaced, you piled a bunch of stones in the right rear side to off set things using weight! At least the car is resting on three wheels! But don’t try driving it.
