RPM Issue

[Romie03]

I purchased a 2010 Infiniti M35x with 66,086 miles on October 27, 2016 from a local used car dealer. The car had service records from the local Infiniti dealer and appeared to be maintained by that dealership. The car was in pretty good shape for the most part but had a few scuffs and scratches. But I love the way the car looks so I overlooked those marks and just wanted to make sure the car was mechanically sound. Two weeks into owning the car, the RPM needle randomly dropped down from 0600 RPMS to 0400 RPMS and quickly jumped back to 0600 RPMS. As the weeks went by the car started doing this more often and when needle drops it does it for a longer period of time before going back to 0600. I was told the MAF sensors were bad so I replaced both of them. I drove the car hard one morning after I installed the MAF sensors. Later that day, the car road like a dream. It drove as if it were brand new. The car was super responsive and didn't have a powerless and lagging feeling. Then the next day it went back to how it was before I installed the MAF sensor. The RPMS drop when I'm in Reverse and Drive, when I'm at a stop light or stop sign, and after the car somewhat aggressively. The MPGs and power has been affected by whatever is going on with the car.

Any suggestions or advice as to what could be wrong with the car would be greatly appreciated! I just bought the car and don't want to sell it next year because of this issue. Thanks!

[BlackCat81]

Clean throttle chambers, perform idle air volume and closed throttle position relearn.
There's also bulletin# ITB10-014a for "engine speed drops lower than expected when decelerating or coming to a stop." It's an ECM reprogram.

[Ilya]

Welcome to the forum!

Do what BlackCat said!

[Romie03]

Thank you for your response! I did the relearn process twice and it didn't do anything. I'll clean the throttle chambers and do the relearn process again tomorrow. I'm little confused about the bulletin number you posted. I searched the forum for it and found it on a post about a member having an issue with his M45. But does that mean my issue is the accelerator sensor like the member with the M45 or could it be something else?

Thank you Ilya for the welcome! I look forward to being an M owner (hopefully lol).

[airmanhoward]

Please post the results when you find out.

[BlackCat81]

Thank you for your response! I did the relearn process twice and it didn't do anything. I'll clean the throttle chambers and do the relearn process again tomorrow. I'm little confused about the bulletin number you posted. I searched the forum for it and found it on a post about a member having an issue with his M45. But does that mean my issue is the accelerator sensor like the member with the M45 or could it be something else?

Thank you Ilya for the welcome! I look forward to being an M owner (hopefully lol).

As far as I know it only applies to the VQ35 motor. I've done the update on a G35 for the same concern. The ECM reprogram is something only the dealer can do, and once it's updated it has to have an idle relearn and closed throttle relearn anyways. They should charge you 1hr labor for it. I'd wait to clean the throttle bodies and see if the reprogram fixes it.

[Romie03]

@ Airmanhoward: I will post the results tomorrow

@BlackCat81: I'll follow your first suggestion and if that doesn't work then I'll have no choice but to take it to the dealer and have them do the ECM reprogram.

[Romie03]

Here's a video so you guys can see what's going on with RPM. https://youtu.be/lqRzgt-skII

I'm going to clean the throttle body after work and I'll post what happened afterwards.

[Ilya]

For the record, BlackCat suggested you first get the reprogram and relearns done before touching the TB's as they are VERY sensitive and you could make matters worse without even trying.

[Romie03]

Ilya, I'm glad you clarified because I was going to do the reverse. I guess I'll be making an appointment with my local dealer tonight and have them do the reprogram. Thanks!

[zags]

I recently took my car in to the dealer and they did the updated firmware flash...now I am having this stall/hesitation when going from higher RPM's to quick stopping and then re-accelerate.

Ughh!

[Romie03]

Here's a quick update on my situation:

I went to Infiniti of Bayside to get the car diagnosed and they told me the car drove normal because no lights came on. I asked the technician if he witnessed the RPM hesitation that I have been experiencing and he said it only happened once when he test drove it. Apparently 3 technicians drove the car and the diagnostic machine didn't pull any codes. I don't think this problem will be found by hooking up a computer to the car because it seems like no one can find the problem with the diagnostic machine. So the technician wrote my car off as "works as designs" but I'm still experiencing the same problem. So I decided to change the serpentine belt and spark plugs (NGK Plugs) this pass weekend to see if that would remedy the hesitation. Unfortunately it did not and I am still dealing with this problem. What I can say is the car seems somewhat more responsive with the new plugs but still feels like its lacking power. And the RPM needle continues to drop whenever I stop.
On top of this issue, the mechanic said he found motor oil on the spark plugs since one of the gaskets need to be changed. Labor alone will cost $450 to change that gasket and I have to buy the part from Infiniti. Then the dealer also said my rear passenger lower control arm and bushing seized and needs to be replaced. Therefore, they could not perform the wheel alignment I was scheduled to get done.
So, it has pretty much been problem after problem with this car since the month I bought it. I've spent more than $2,000 on this car and I haven't even made my first car payment yet (thanks to a program I'm in at my credit union). I want to trade in the vehicle and go back to Honda/Acura because the MPG is really killing me since I can't find the problem (averaging 13-14 MPG on the highway= 250 miles out of each tank) and I only do highway driving in this car (85 mile round trip everyday).
Thanks everyone for your input and advice to try and find this problem, peace!

[Romie03]

I recently took my car in to the dealer and they did the updated firmware flash...now I am having this stall/hesitation when going from higher RPM's to quick stopping and then re-accelerate.

Ughh!

That sucks because I'm sure you took the car in to make it more efficient and the update made it worst. Did you try taking it back to the dealer to see if they could find what went wrong?