Posted this on G35Driver without any responses.

I have been having vibration issues with my car while driving on the highway. Most of the vibration is felt through the gas pedal (like a foot massager). Shifting gears could also be a lot smoother. I have replaced just about every suspension part and my rear diff mount is not leaking. I have been annoying with posts on here because I do not know what is causing this feeling. Feels like my car is going to break apart over bumps and every small crack is felt through the gas pedal.

Another example...if I'm going 70 on the highway, back off the gas for a second, then just tap the gas pedal slightly the whole car jerks like the drivetrain is trying to catch up to the wheel speed. The whole car feels like it lurches forward and backs off. Kind of hard to explain.

Here are videos to show how much the engine moves. I'm pretty sure it's banging too as the whole car rocks when I rev it in neutral.

http://www.youtube.com/watch?v=l39pm68I3fY

http://www.youtube.com/watch?v=gF_UWjo3MFw

Thanks,
Aaron

 

AND I looked at both engine mounts without seeing any cracks or fluid leaking.

Is it easy to replace engine mounts? I can't imagine how I would get to the upper nut directly under the headers!

 

I don't see what I would call excessive engine movement when you're revving the engine.

Can you get to the mounts well enough to take some measurements or pictures to compare to a known good mount? Another possibility is to measure the position of the engine relative to the body on your car and compare it to one without a vibration issue.

I've felt a very slight vibration in the gas pedal since my car was new. Since there's no mechanical connection between the engine and pedal, it's probably just a harmonic response in the body. It varies with engine rpms, not vehicle speed.

How old is the car and how many miles on it? AT or MT? Accidents or mods?

I've driven some used Zs that have flat spots in the gas pedal where pedal movement doesn't cause the engine speed to change, but it'll change abruptly when you move past the flat spot. I think that may be part of your problem.

 

I know there is no mechanical link between the pedal and engine. It can be felt through other pedals too, but I don't think it's as bad. The vibration and clunks through the pedal seem to not vary with RPMs. I'll be at a constant highway speed and when hitting a change in pavement height (where the new pavement starts, higher then the old) I feel all the feedback through the gas pedal. The suspension is solid over bumps.

I'll take my foot away from the gas pedal and feel a totally smooth ride without any problems. Having my foot constantly pushing the pedal while it vibrates like it's connected to the road is very annoying.

The car is MT, has just under 140K, hit a curb and a deer.

 

The flat spots I can notice where no power seems to be usable at a certain RPM. The responsiveness isn't a big deal, the engine and drivetrain seem loose at some times. I couldn't see any tears in the transmission mount after a quick inspection.