What can cause the tachometer needle to drop after letting off the gas?
 

Hi yall, so i have a 2003 350z that's been running great until recently its been having a misfire i think? When i turn it on when the engine is cold it sounds great and the idle is fine. But when the engine heats up to normal operating temperature and i'm driving it, it starts having a misfire. When it gets into second gear, the engine will do a low hum and you can feel the power disappear and won't accelerate no matter how much you press on the accelerator until you fully step on it. When the engine hums and i let off the gas, it will jolt a bit and hum loudly while the rpm needle very slowly goes down until it gets to 1k and plummets before jumping back up to regular idle speed. At 2k RPM i let off the gas and the needle while plummet down to 900 rpm and then jump back up to regular idle speed. Any ideas what it could be? Here's a video before it got even worse recently

I know what your problem is... youre letting off the gas pedal

Can't step on the gas without risk of the engine blowing up