:? I need some suggestions. I have a 91 Bonneville in excellent shape and mechanically sound, although it has 200,000 miles. All of a sudden when you accelerate from a dead stop it vibrates really hard, almost feels as though you are riding on rumble strips for about 2-3 seconds then it stops and runs fine. Anyone have this problem or have any suggestions on where to start? :? :?:

We're gonna need more info (and welcome to the Boneville Club )

Does it feel like a suspension/steering thing, or is it an engine trans vibration? Being accelleration dependent, I'm betting engine/trans.

How old are your plugs/wires?

The plugs are new the wires I am not so sure. The plugs were replaced recently because the car would "slip" or miss while driving. These two things may be related but I am guessing not. I am not so sure what type of vibration actually, how would I tell the difference?

Most 'stumbling' or vibration problems with the engine itself are ignition related. Anything from the ICM to the plugs (with the coils and wires in between).

Wires are usually only good for about 50k miles. As a general rule, if you suspect a problem like this, and don't know the age of your plugs and/or wires, it'* a good idea to change them.

To go even further, most of these problems can be solved by a full tuneup. Plugs, wires, fuel filter, air filter, PCV valve.

This isn't to say that your problem is coming from there, but it'* common. Get a helper to put your car in gear, set the Ebrake, and rev the motor IN GEAR with the foot brake applied to the 'suspect' rpm range. Do you see a vibration in the engine?

The engine runs and idles fine. Everything but the wires were replaced. I have had a mechanic look at it twice and he says the steering parts look ok and he has replaced the crankshaft sensor but he isnt sure where to go next. It sounds great until you start to move the car.

Does that vibration seem to affect the power? Even a little bit? This really sounds like an 'under-load' miss.

And we are sure its not the tires scrambling madly for traction under the extreme torque of first gear right?

That'* a good possibility too, Rogue.
Keep in mind, an intermittent miss on a single cylinder will shake the bejesus out of you under hard accelleration.

Hub/bearing, tie rod, ignition, traction, all these can be factors. We need to get alot more analytical here, and to do that, we need more information, or at least to start ruling things out.

With your symptoms (and not having the luxury of test-driving it myself) I'd change the wires right off. They probably need it, anyway. Inspecting all 6 plugs would be good too. If one or two look different than the others, it could point to an ignition problem farther upstream.

Does it only do it in first gear? Can you accelrate hard in other gears with no problem?

!st gear coulld be slipping...

well it does it only in first gear, it shifts fine in the others. Wires will be the starting point. Maybe a thorough inspection of the steering parts will be next. Lets see how it goes in the morning when we start with the wires