Hello, I would like some advice on what I've noticed on my 08 350z. Say I am in neutral and rev the engine to about 2k+ rpm. After taking my foot off the pedal, the revs will drop and then stick at around 1300-1500 rpm for around half a second. After that, the engine returns to idle of around 650 rpm. I also observed that the engine tends to hesitate more especially at lower RPMs. Additionally, the car will jerk forward when reaching around 1200-1500 rpm (depending the gear I am in) before then falling to the idle rpm range. It is difficult to describe but I can get videos and obd data if requested.

This began occurring after doing a replacement valve cover gasket job. What had happened is that the car kept going into limp mode after the repair. I thought it was me failing to do the idle relearn procedure, but it actually was a disconnected vacuum hose. I cannot remember the code it was throwing. I also do not remember what exact hose it was except that it was near the throttle body. I am wondering whether performing the relearn procedure while having that hose disconnected may have partially bugged the ecu. I have replaced the throttle bodies and done the relearning to no avail.