I hope you guys can help me out. I have a 94 Z28, 77K miles, and its a M6. The car seems fine for the first 3-4 minutes or so, but after that, it feels like the engine starts rocking back and fourth in relation to the car. This happens at any speed and any gear. The key is....it always happens around 1200-2000 RPM while I'm cruising at a constant speed. If the clutch pedal is pushed in, the rocking problem will not occur at all. I just came inside after replacing the trans mount, but that didn't help. Also, the engine seems to make plenty of power. Any ideas would be very helpful. thanks

 

Anyone?

 

That's gonna be a tough one without a better description. Could be motor mounts, or something loose, or maybe you're feeling a hesitation/stumble, driveshaft vibration, etc?? Does the motor move abnormally when you rev it in park?

 

No it looks fine when its in neutral and the motor is reved. The car only has this problem when it is in gear, and cruising at a constant speed.

 

Sounds like a driveshaft problem. Time to upgrade!

 

In my experience a vibeshaft will get worse as you increase speed and really doesn't shake until higher rpm's. Perhaps an ignition problem is giving you a stumble at low rpm's. I can't imagine a 'rocking' though. Perhaps a better word is 'vibrating'?

What changed when this started? Anything?