So few month back I bought a 2011 g37xs coupe The car has 75k miles on it and really stunning. Ever since I bought the car I’ve been noticing a lot of behaviors that are dangerous and became annoying to the point that I’m posting this right now. Let’s start with the problem and guys be nice I’m new, from cold start the car seems like it has some sort of a hiccup like drops 500rpm for a split second not really annoying but now it occurs while driving, the car would be cruising and I press the gas and it feels like it’s cutting fuel to the engine for a split second, another thing is after driving for a little and coming to a complete stop and then going back on the accelerator the car seems like it’s dead unless I push the accelerator more than 30% you can see the rpm’s go up but the power isn’t there until it wakes up and acts normal again, another problem is driving thru traffic and jumping from break pedal to accelerator the car bucks back and forth and feels like it’s hitting walls, this happens often but I cannot recreate it same with the other problems they are there but they happen out of no where when it bucks like that it feels like my differentials are getting stuck or someone put a stick in my wheel lol, and sometimes it happens when I push the accelerator the car feels like I hit a wall then downshifts and accelerates, btw I tried both D and DS it does it in both, another problem is when I’m in manual mode and And I’m shifting through gears it’s fine but when I want to do a complete stop and I leave the car in 2nd gear the car would literally hit a wall while automatically shifting to 1st and in worst cases the car would do that and jump forward, I was in my friends same car and his car didn’t even feel like it’s shifting to 1st you can just see on the screen 2 become 1 no jumping or hitting wall, this problem I can recreate because it happens every time I don’t shift manually to 1st and let the car do it itself, I feel like this problem is connected to the other problems I stated , another thing is when I’m cruising and I start to slow down I can feel the car downshifting awkwardly where it makes me move forward, my friends car didn’t do that or while I’m driving the car just decides to downshift for no reason nothing I do triggers the car to down shift like I’m no pressing gas or breaking it would downshift and hold rpm’s and shift up in line 15 seconds and this is happening in D. Things I already did:
1.changed the trans for one with 30k on it
2.took it to dealer to flash the TCM to new update and the ECU
3.changed oil
4. Changed air filters
5. cleaned throttle body and MAF sensor
6. changed all of my fuses to brand new fuses
7. Changed the fuel pump and fuel sender unit
8. changed the AC control AMP
9. did the ECU reset and throttle body relearn
after the echo reset and the throttle body relearn the car behaved better but after I drove it for 3 days all of the problems are back
I’m really lost and don’t know what to do
Anyones help would be appreciated.

 

At first it sounded like common misbehaving transmission but the fact that you have already changed it and the problem persists is puzzling.
For further assurance check fluid levels on this new trans and make sure it's level.
For further diag you'll need to get some additional data confirmed.
They sell affordable bluetooth OBD2 readers that can communicate with your phone and you'll be able read additional parameters.
One thing to look out for is fluid temp which can be read with the APP, if fluid is overheating it could explain your troubles.

The rest is looking at the data and seeing what these sensors are registering since at 75k there is not much that breaks down that could cause this however this is the typical mileage that gallery gaskets start failing and could be impacting your VTC angles not letting the phasers advance with the throttle angles as they should.

 

hello and thank you for your reply, I have the scanner set up with my phone and there isn’t any codes being thrown but I will check on the fluid and the temperature of the fluid, however I’m not sure how to check the fluid level of the transmission since there is no dipstick for it
as as far as I know the engine is in a pretty healthy condition and when these things happen it keeps pointing me to look into my drivetrain like differentials and transfer case. I’m even thinking it could be the motor mounts or trans mounts since it’s a car from 2011

 

Those things you mentioned seem about the same on my 2011 G37x coupe. For the bucking in traffic, you can reduce it by adding a differential brace which I did and it reduced it by a lot. I have a post about the differential brace that I got. Bucking from 2nd to 1st is pretty common, it even does it on my 2013 528i. And for the cold warm-up drives that are pretty common, you have to wait for the transmission to get up to temp, which will also increase the temp in the transfer case. If anything change the front and rear diff fluid, as well as the transfer case fluid. Pretty easy job. Also, to cut the lag off of the car and make the throttle more responsive you can get a pedal commander or a tune and it is a night and day difference.