Had a mechanic recently replace the head gasket on this engine due to a leak. Few weeks prior to that spark plugs and fuel injectors were replaced. Now it is severely hesitating when i try to accelerate almost like a lack of air or fuel. If i slowly press on the gas to build up speed there is no issue. Any ideas on what I'm dealing with? I plan to take it back to the mechanic so he can troubleshoot but i have to manage it for a few weeks due to me needing the car for work. Don't see a video attachment option so i posted the video showing the hesitation as i try to speed up below


https://drive.google.com/file/d/19BtmF4 ... share_link

@AliefZee My 2009 G37 is having this same issue. Hesitates @ 2100 RPMs. Were you able to find a solution?

I tried pretty much everything you did, then handed it to a mechanic. He took the engine apart and still couldn't resolve the issue. Odd thing is, after a reset, it runs fine until the engine is shut off. Once you turn the engine back on, the stalling at 2100 RPMs resume.

He's wanting me to buy the VVT sprocket and timing kit, but I'm hesitant to spend that money and still unsure it will solve the issue.

That sounds suspiciously like a firmware or "reduced power mode" problem and not a mechanical issue. After a head gasket replacement, it's entirely possible one or both VVEL sensors are out of calibration (many independent shops either don't know about the adjustment or don't have a capable scanner). Have a dealer or someone with a high end tool scan all the systems in the car, and if that doesn't turn anything up, try a VVEL adjustment. If that doesn't help, try having the ECM reflashed. Corrupt flash isn't terribly common, but it does happen.

Yeah, I was thinking the same thing that it's something doing w/ the onboard computer and not mechanical. I told the mechanic and he had the firmware checked out and he said it was fine.

I'll do some more reading on "reduced power mode" to see if it fits what I'm experiencing.

Thanks for your input.

"Reduced power" is something in between normal behavior and a flat out limp, it's when the ECM disables some systems and not others as part of a failsafe. But it usually happens in response to a DTC (although not necessarily an engine DTC). The VVEL has its own controller separate from the ECM, that's why I suggested you need a thorough scan. Vis the firmware, if it's corrupt and going "off in the weeds", the only way to tell is to reflash it and see if the problem goes away. Verifying that the firmware version is correct doesn't tell you if the code is executing correctly. Some years back we had an older Altima that would perform just fine until it hit exactly 2500 RPM, then it would die momentarily and then resume in a constant loop, up-down-up-down. There was an instruction someplace in the firmware which only executed at exactly 2500 that would send the processor into la-la land, then the internal watchdog would reset it, then it would la-la at 2500 again in a constant cycle. We refreshed the flash with a copy of the existing program and the customer had no more problems. One corrupt instruction was invisibly causing the whole issue.

I sure hope that's all it is, or something simple, because i'm nearing the point of throwing my hands up. The engine runs so smoothy otherwise, and that's why I want to get it fixed. As long as I don't hit 2100 rpm as the gears shifts, I can get it up to 70mph. Once it get there, it will hesitate again if I push it further because that's when it needs the extra RPM to go faster.

Thanks again for sharing your experience, VStar.