Rpms work fine for a couple mins after replacing IFS but then they go haywire and back to 0

[Bigrob]

Hi, I'm new here and after reading about some cause of tacho reading 0, I determined my ignition failure sensor was shot. I got an aftermarket part for it and replaced it and the rpms read fine for about 5 mins, after that the needle goes all over the place and dies back to 0. If got some suspicions about the quality of the replacement ifs and my initial guess was maybe the crappy sensor gets too hot after a couple minutes of running (considering its mounted to the side of the block) and then dies? Idk if this seems plausible but I wanted to check here for any ideas before I end up buying another sensor ( hopefully oem this time). Cheers!

[jalalcool12345]

from where did you buy the IFS sensor? you said you're suspicious about the quality