Vibration on Acceleration

I have a '96 Olds Cutlass Supreme with a 3.4L V6. The past week or so I've been noticing a vibration when I step on the gas going down the road. It doesn't do it from a stop and I step on it, when I am cruising along and
want to accelerate I feel this vibration that I can feel all the way through the steering. It comes and goes.
Can this be the transmission, drivetrain, loose motor mount? I am stumped.
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I get the same thing in my '95 monte z34. Comes and goes. I was going to change my timing belt to see if that helps any. My tires have been balanced, brakes have been changed and tranny fluid/filter has been changed recently, so I checked those off as culprits.
Steve

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Geoff,
Yes, a timing belt. This is the 3.4L dual overhead cam engine. It has a timing belt, not a chain.
GMdude
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I believe the lower cam is a chain, the upper cam is a belt.

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Nevell Lewis wrote:

Check the plug wires ohms when at hot temperature.
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I'm going to see if it does it when its "cold". Its just the strangest thing, the vibration it makes is like if you were going over highway rumble strips, but, the tachometer never jumps, I would assume it would with a miss or low ohms on the wires???

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This could be a bad inner cv joint, causes the drivetrain to "shudder" on accceleration only.

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Could be tires out of balance or a broken steel belt on a tire. Have them rebalanced and checked

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Could be a cracked flex-plate. (cranking gear)
This happened to me several years ago. I went through all the suggested items that the other posters mentioned to no avail. I was sure that it was piston or connecting arm related until I tried to start the car up one morning and all that happened was that the starter was spinning. A doughnut size piece of metal broke off the flex-plate where the engine mount bolts were.
The flex-plate was only $46 but I had to pull the trans out to replace it. 2 days work in my home garage.
Hope this helps.
MIKE....
wrote:

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