I bought one from ebay and I tried to put it on and it didn't work. Car wouldn't stay on. I changed it back to my old MAF sensor and now I am hearing this weird hiss noise in my engine and when I put it in park the RPM goes up a bit. Also when i let go of the gas while driving the RPM cranks up and down and up jerking my car. What can be the issue? Any help would be great. Thank you.

 

my guess would be maybe u caused a vaccum leak somewhere....i did the smoke test on mines before to find out where it was coming from