well i dont know if this will help but i had a misfire problem also. it was a vaccum hose that was loose under the hood... if this is the case when you put the scanner on it should come up with an evap code.

 

Have you checked your coil packs?

 

I have a 02 3.8 - Coil pack was messed up - replaced it - Ran like new.

 

i just now replaced my coil pack and it wasnt that, but i did find out that it is the plugs/plug wires that arent firing on the middle coil pack. them plug arent getting any fire at all, i called berglund and tlkd to a guy about it and he said its the thing that the coils set on (i forgot the name of it) has gone bad, and is pretty common on my motor to go bad. i called advance auto and they said they have it for $128 bucks. so i think ima try that

 

the part is the ignition control module

 

Multiple cylinder misfire could be caused by a lean mixture. Make sure that the upstream sensors are working properly. They can get lazy, so you will need to look at the activity with a scanner and make sure the voltage is changing at a rapid pace. Steady reading indicates a bad O2 sensor. Also take a look at the fuel pressure and make sure it is within specs. Also the ignition control module (under the coil packs) can go bad and cause the engine to run really crappy.