Changed the spark plugs on my 2002 gs300 and put everything back together, started her up and now she won't run. I'm getting a very rough idle and then she just shuts off after about 4 seconds. What could this be? The plugs are ngk iridium's and I do believe that these are the right plugs for this car.

 

If all you did was the plugs then it's a pretty easy answer... Either one more more plugs are bad or don't have a good connection to the wires. Redo it.

That or you knocked something unrelated out of whack during the swap.

 

coil packs maybe? also could be bad sensors on your manifold. Any check engine lights? Run the codes if their (and their should...) are and look them up.