I have a 2004 G35 Automatic, 23500 miles, oil changed ever 3 months at the dealer, K&N air-filter installed at 22,400 miles, tires rotated twice at 10k & 20k and in-cabin filter changed at 15k. No other maintenance done so far.

I have noticed for the past month, the car is not smooth as it use to any more. I can feel vibrations in steering even at park and while driving it gets worse. I can feel minute vibrations in the accelerator and brake pedal as well. Has anyone else had similar experience?

Also what has been happening recently is that if I am driving on a flat road at 40-45 miles/hr at 1500-1700 RPM and there is a slight upward slope, the car jerks quite bad. It feels like the gear is downshiffted, but the car is pushed forward as if it misses or something. Anyone else experienced this? If so, what might be the issue?

Thanks for any insight.

 

I have not experienced the problems you describe but here are some possibilities: Your engine vibration could be a broken motor mount but please realize that most cars loose their smoothness as they age. Your transmission/downshifting issue sounds like your torque converter is locking at the wrong time.

Your first step is to take advantage of your warranty and have the dealer check these problems out.

 

I don't know about all your other problems but I know there have been a lot of other posts about people complaining that the automatic is jerky around 40mph with light throttle. It feels like the car can't decide whether it wants to downshift or not. My '06 X with 2,500 miles does it too. I think it's just a design flaw with the tranny and nothing can be done about it. If you do a search of the forum you will find that this is a common problem.

 

I would check the motor mounts first. Hope it is an easy fix.

 

Similar experiences, went away when I installed Gordee's grounding wire set. I suspect the grounding properties diminish over time.