MacBook Air extremely slow without Touchpad flex cable attached

My Mid 2012 MacBook Air suddenly stopped working properly. First, some of the keys did not respond or were sending keystrokes repeatedly. For example, the power button was presumably hit and the device turned off. I tried resetting the SMC and NVRAM multiple times, but to no avail.

I tried booting into recovery mode. I had a firmware password set and I could not enter it due to the keyboard error. Sometimes, after not using it for a while, I could enter it but it would not finish booting but just turn off while booting.

So I decided to open it and I removed all parts from the case. Then I only put back everything except the keyboard and I did not attach the touchpad flex cable. I connected the MBA to a USB keyboard and mouse and an external monitor. The device booted successfully, but at an extremely low speed. It is so extremely lagging that it takes several minutes to start Safari for example. Also, the fan is always running high, even just after starting the device. A temperature sensor app I downloaded showed normal temperatures for the CPU and other parts.

So I am not sure where to proceed now. I accidentally broke the flex connector but I could buy a new one, but I would like to know whether the problem is with the logic board or the parts that are not connected right now (Touchpad and keyboard). Is there a temperature sensor in those parts so not having it connected makes the device throttle down? Would getting a new keyboard or touchpad fix it? When the touchpad was still connected, it seemed to work fine.

side note: Four years ago i had water spilled on the MBA. But after opening and letting it dry it worked fine. Can this still have any effect even after so many years running without problems?