Originally Posted by 1slow370

for the mysterious errors like this quick checks are if autoparts stores near you will check the codes for you to see if there is anything pending that isn't persistant or severe enough to throw a light. next step is to get your battery load tested to see if it can hold enough amperage to run the car properly, the voltage may be there from the alternator but get the battery load tested to make sure it can pass all the power on to the car (don't know if i'm explaining this one properly but these car demand a huge amount of electrical power and as you start to lose that things can get a little funny). These are just some quick checks you can do for very little or no money and they catch a lot of missfire issues. I personally had a battery running 13.9 volts was getting a misfire and after a load test on the battery and replacing missfire was completely gone.

If that fails to show a problem then yes you're going to be stuck at the dealer and trying to put up with their BS