05 Nissan Altima HELP

I have an 05 Nissan Altima with 106,000 miles on it. I am starting to have some problems with it now. When I start the car, it is chokes a bit and the ‘Service Engine Light’ keeps going on and off. I took it to the Nissan dealership and they told me that it is a P0303 code, which means that coil 3 is misfiring. So they replaced the spark plugs, and I think they also switched coil 2 with coil 3 just to check if the problem is in fact with coil 3. Thinking that the dealership would charge me too much, I took it to my mechanic’s. He told me that he thinks it is the fuel injector. I’ve also put the fuel cleaning system in the car. The light has gone on and off throughout this whole ordeal several times. Now i am having the same issue again the check engine soon light is back on. If anyone has any thoughts, please help me.

What is the code, now? P030x?

My mechanic told me that he got the same code after nissan people switch the coils around.

Can you feel misfire, from time to time? Try a swap of the fuel injector, with another, to see if the code moves. Be sure to erase the old code before the test drive. http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c152801afc4f

take it to autozone and get the code pulled free.if it shows misfire it could be the plugs,wires or coils