For anyone who may still be having this problem, I have just fixed the issue for a MacBook Air I am working on. I tried all the PRAM resetting, deleting plist files, terminal commands, removing bluetooth devices and checking for viruses of which none of those methods worked. I then turned to hardware as my issue, I removed the bottom cover and the battery then proceeded to remove the trackpad flex cable. Once I had removed the flex cable I flipped it over to see the pins on the under side of the cable, I noticed on the motherboard side there was some black dust or debris or something on there so I cleaned that off with some isopropyl and a cotton tip and put it all back together and there you have it! It is all working for me now with no issues.