Altima Shakes During Idle And While Driving. Service Engine Light Comes On And Then Goes Away

Hi. I have a 2003 Nissan Altima with about 93,000 miles on it. About a month ago, I turned the engine on and the entire car started shaking. The check engine light was blinking. There was no noise, just shaking. I noticed that as I sat there with the car in park, the RPM was jumping around without me touching the gas pedal. I sat there a little while longer (about 5 minutes) and it stopped shaking and the check engine light went away and the RPM went way down and stayed down. For several days, everything was fine. Then it happened again. Only the car was warmed up and I was sitting at a stop light halfway across town. Then it was fine for another couple day. Then one day, I was on the highway going about 60 mph and it started shaking again and the check engine light went on again. I had also noticed that I seemed to be going through fuel a lot faster than usual. I felt like I was filling up the gas tank all the time.

Annoyed and worried, I took it to AutoZone to do a check engine light diagnostics. They got the code and told me cylinder 2 was misfiring. They said I needed new spark plugs and to run some fuel injector cleaner through the gas tank. So, I took it to a mechanic and paid for them to replace the spark plugs and put the fuel injector cleaner in the gas tank. They recommended a tune up, so I also had a new air filter and serpentine belt put in as just a general maintenance thing. They said everything else looked great.

Well, it ran really good…for about two weeks. Then yesterday I turned it on and it was shaking really bad. The service engine soon light was flashing, and it didn’t go away within a few minutes like it had done in the past. It continued to shake, and the service engine light continued to flash for the majority of my drive across town. It seemed to be worse when i was idling at a stop light. When I got on the highway, I had trouble accelerating. There didn’t seem to be enough power. The car surged forward a little bit as I tapped on the brakes when I made a tight turn. It was a little scary that it did that. I had not noticed that before. I finally stopped and shut it off. Then, about 20 minutes later, I turned it back on. No shaking. No service engine soon light. I drove home without any problems. I’m not sure what’s going on.

Some people have told me it’s the fuel injector and others have said it’s the ignition coils. Any thoughts? The shop I brought it to before never really did an official diagnostics themselves (Auto Zone gave me the code and the parts) so they said they will charge me $79 just to figure out what the problem is. They said it could be upwards of $400 for the ignition coils (just for the parts!) and $600 or more for new fuel injectors. I get the impression that the only way to know for sure is by process of elimination-trying new parts until something works. Does anyone out there have any thoughts? I’d hate to get all kinds of parts I don’t need before I figure out what the problem is. Please help! Thank you!!

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