My car shakes a little bit, back and force, on high speed like 60-75 miles. I feel it on my driver sit. I balance tires twice and it did not help. I went to Nissan dealer (I did not have Infiniti near by) and they said it might be powertrain and suggested to go to Infititi dealer. Also, I have check engine light (random misfire code) appearing every 3 months. I replaces spark plugs and but the light still appears randomly after drving 2K when I start a car, only when I start a car.

I wondering if anybody can suggest based on previous experience how I can differentiate between powertrain issue and random engine misfire. I am trying to figure out what causes car shaking a little bit on high speed,where to invest money

I have g37s 6MT 2009

 

Go to autozone or similar to get your codes read. That would be a starting point.
A misfire would cause surging/hesitation too which could be construed as shaking.
Could also be something trans or trans control related.

Get it properly diagnosed.

 

I have the same problem at high speeds. I went to the dealer and they said my U-Joints are worn (did not tell them about the swaying so may not be the cause). Recommended that I replace the drivetrain. Didn't do it since they wanted to charge me 1.3k to do it but I did have a mechanic look at it and he said there is a little play in them but that it wasn't a crucial fix. Lemme know what you find out im curious

 

Sounds like drive shaft or u-joint, or something along the line of where power is transfer from engine to the wheel. I experienced something like this in my other car (not the G or Q).

 

Do you have aftermarket wheels? If so you might need hub adapting rings to get rid of the vibration.

 

Is the vibration consistent or does it go away after everything warms up?

 

thank you for your replies.

I have original wheels. The code for engine check engine "Random misfire".

The vibration is small. It is pretty consistent but it happens only on high speed, like 65-70miles/hour. I do not drive on highway every day, so I do not experience it all the time. If it continues, I'll go to mechanic or dealer.