96 Monte Carlo Idle Problem Help!!!!!!!

My girlfriend has a 96 monte carlo ls with the 3.1 engine. The service engine light came on and the car started to idle rough. It is reading a misfire. It gets worse every day. It shakes when in drive with your foot off the brake. It takes off great how it's supposed to but the idle is horrible and it feels like the engine is going to blow up. I reset the light twice and it went back on only when it idled. I already replaced the plugs, wires, and coil packs and none of them did ANYTHING. The firing order is right. Does anyone know what the problem is?

Mine is the 3.4 engine, but i've been having nearly the identical problem. My car would idle, not rough, but the engine and to a lesser degree the car, would shake when in park. taking off from a light, the car would feel like it was either missing, or just not getting much power until up around 35 mph, then the car would accelerate fine.

I just replaced my plugs, and that seems to have taken car of the rough idle for the most part, though when driving it right after, the car did hiccup once.

Now, i just bought the car, and the previous owner was of a dubious nature car whise, i don't feel he treated this car very well- it has a couple dings in the front quarter panels, and the coolant is extremely murky, despite having been drained and replaced. now, if it weren't that i'm away from my normal "car fix'n place", i'd have the heads off in a jiffy.

did you throw a scanner on the car to check the codes?

I wouldn't hesitate to say bad injector

Use fuel injector cleaner at least once a month and all your problems will be solved. If you want a good fuel injector cleaner, use Lucas Fuel system cleaner. It's available at your local AutoZone for under $5 bucks!

thanks for the advice!