Idling a little rough

when I start the car it idles really rough, but after I warm it up and drive for a little while the problem subsides. When I'm sitting at a stop light though, you can feel the car shaking a little from the idling, and it also makes the muffler rattle (but its blown and I'm replacing it soon)

If you could give me some more insight as to why the car idles roughly please share that information with me.

Could be any number of things...
-Garbage sparkplug wire(s)
-No good sparkplug(s)
-Worn out cap and rotor

I would check those first. Also, what year is it? If you have EFI you'll want to check some other things.

its a 95 Z34, when I bought the car the guy I buoght it from said that he thinks the problem comes from bad plug wires. from what I've read 3 of the plugs are in a odd and hard to get at place, so is it going to be a difficult thing to do to try and change the plug wires

I had the same problem with my monte. I replaced the wires and did a fuel intake clean for $330 dollars and that didtn fix the problem. I took it to the dealership and they said it was the fuel pump, fuel filter and OZ sensor. $1400 to replace all. I took it to another shop and replaced the fuel pump and filter for $400 and now it runs fine.