Nissan Repair: Engine misfire, nissan maxima gle, ngk spark plugs

Question
Hi Von
I have a 1999 Nissan Maxima (GLE) that has an engine misfire at times. I can feel it when I come to a stop...but not all the time. I don't feel it while driving. The car has 65,000 miles on it so I changed the spark plugs. The plugs looked ok, but had a strong smell of gas. There was still a misfire problem after I replaced them. I used an engine scanner and have 2 "pending" trouble codes. PO325 (knock sensor) and PO300 (random/multiple cylinder misfire) I took it to a repair shop and the owner said I made a mistake by not putting in NGK spark plugs. He said the problem might have been from the original plugs and by replacing them with Champion plugs could be why I'm still having the same problem. I went to a parts shop that was a block away to buy some NGK spark plugs. The owner of the parts shop said he didn't want to talk bad about the repair shop because they are a good customer, but thought that didn't sound right. He said if it was him he wouldn't replace the plugs. I use to be a mechanic in 70's and 80's and do most of my own repairs. A lot has changed, but I've been able to keep up by asking lots of questions. I'm on a limited income and would like to fix this myself if I can. Any help you can give me would be a great help.
Thank you,
Edward  

Answer
There are two things that can cause this.  The first is the coils and they are known for going bad.  About $300 bucks for all six and since you changed the plugs you know where these are at.  The second is the fuel injectors.  I have a 350Z and the fuel injectors were plugged up and that caused the mutiple cylinder misfire.  If it were me the first thing I would do is test the coils for the proper ohms rating and if that was not the cause I would power flush the injectors.