It needs spark plugs and wires and a dist. cap and rotor very bad. It's been on the same ones since probably 2000 or so. I'll get the maintenance done this week, I ordered plugs/wires/distr. cap & rotor so they'll arrive this week, and I've been thinking that this tune-up would solve the problem. Is that possible, when a car needs a tune-up badly, for it to behave this way?

The shaking happens different times:

When I start accelerating, depending on how hard or easy I go. Basically, if I give it just a little gas, everything is smooth. Or, if I give it more gas than would be normal (kind of a "jackrabbit start" but not a very strong one - just a little more of a jumpy start than would be normal) then again everything is smooth. It's in that MIDDLE area - not a very easy acceleration or stronger one, but right in the middle, what would be "normal" usually.

Once I'm moving along, it's the same story, no matter what gear I'm in (auto trans) or how fast or slow I'm going, if I give it a LITTLE gas or a LOT it's smooth, but if I go right in the middle, a "normal" acceleration, it vibrates.

When I've been idling I've revved up to see if it happens (to eliminate that it would be the trans, which I didn't think it would be anyway because it shifts smoothly for the most part.) Well, when I get the tach up to about 4-5,000 RPM it starts to do this rough idle/vibration also.

It makes me feel almost like it could be a timing issue - is there a way of adjusting timing?