So I've seen lots of questions and videos about people having issues with hesitation especially in the lower RPMs or it doesn't go past 3k rpm when accelerating. I couldn't find any solutions and what I found it either worked for a day or not at all. (See Below)



Things I found when troubleshooting the issue:
Valve cover leaked oil into spark plug well #5. (Replace whole cover/gasket)
Black throttle bodies (cleaned with throttle body cleaner)
Old & oil on spark plugs (changed all plugs around 97k)
upper plenum gasket leaking oil (replaced gasket)

nothing worked after all parts replaced.

Aftermarket parts:
Tomei catback
injen long Tube CAI

Troubleshooting methods:
idle relearn, battery unplugged for a day, ecu reset, checked for air leaks, checked for codes, changed oil, throttle body reset.

I wasn't getting any codes, so I took it to a shop and did a diagnostic test. They said they couldn't find anything wrong with the car (waste of money). I knew the AFR was off, so it had to be fuel, spark, or the airflow causing the issue. So I pulled the plugs that were pre-gapped out of the box and found out they were off, I re-gapped them to spec 0.043. Finally the car was driving like new even in the rain, cold, and foggy weather where it would usually act up it didn't. There was no hesitation!

Sorry for the long post, hope it helps any one experiencing this issue.

 

I have a similar issue on my daily (m35) I will pull the plugs and regap!

 

I also found out that I have low oil pressure so you might need to replace the gallery gasket if not then I hope the plugs work. Cheers!