Chosen Solution
’''
My Macbook Air, 2017 suddenly started to lag and freeze. The bootup takes over 2 minutes. Youtube wont run on Safari. I ran the the TG Pro test and every sensor seems to Update (10/02/2019) Etre Report
Same result after a clean install points to a hardware issue. Being a pretty recent Mac I’d find it strange if it was the battery but one never knows and I’d recommend downloading and installing Coconut battery and post a couple of screenshot adding them to your original question: Adding images to an existing question Other than that we get into board issues, had an Air for repair not long ago that had a faulty CPU current sensing circuitry giving exactly the same kind of issue. Try opening up your Activity Monitor in Utility folder, select it to show “all processes” and post what it is you see keeping CPU busy all the time. I’d bet on “Kernel Task” in this case..
I had the similar case in my practice, there was an issue with the SSD. I would try to load the clean system from the known good external drive (ssd is better), to exclude the ssd failure. In many cases software diagnostic won’t show SSD problems.
Your system has both thermal and voltage sensors and both can cause your system to go into CPU Safe Mode. This is where your CPU’s clock is lowered to keep the system from overheating. This is when the Kernel process is consuming a lot of threads. Most of the time we see thermal issues or a bad/disconnected thermal sensor. I would install a good thermal monitoring app to make sure that’s not the issue like TG Pro using the free version will allow you to see the thermal sensors and fan. A common cause is liquid damage into the keyboard or trackpad or on your logic board’s voltage sensor has failed or the voltage divider logic is bad.
Please click on the hard drive icon, then go under File to “get info” and tell us your results.
Sound like a software problem or you maybe low on system storage, does it ever tell you your start up disk is full? I would try to backup your data and then do a wipe and reinstall of Mac OS X
