I have a 1.5jz in my mk3 supra and when I go to start it up it backfires and carrys on then I noticed on the laptop the rpm signal while cranking is 0 then for a second is 400-500 nothing in-between, once it's running the rpm signal is perfect, using a timing light it's spot on and drives well, could this be an issue with the crank sensor itself or something else?