I don't know if anyone here remembers but I was having some problems with my local nissan dealer cuz I took the car into them because of a hard miss when I did a cold start and sometimes the car would shut off if I shifted it out of park. They kept my car for about 7 hours and checked the ecu and couldn't find anything and the mechanic told me that my only choice was to "bring the car back when it got worse" and then they told me that the car runs super rich when I they did a cold start and they sent me on my way. Well I continued to live with this problem for months and I think I discovered the problem. I realized that for a couple of months my car was running with platinum plugs that I shouldn't have had in there but that is when all my problems started and I've run premium from day1 and I finally switched my plugs to stock NGK's and was still using premium and there was nothing better to report and I was pretty much lost after that. Well one day last week I was sitting at work reading my manual and I noticed that the manual didn't specifically say to use premium at all times but it did say that premium is good for the car nonetheless so I decided to do a little experiment and my tank was empty anyway so I drove down the gas station and filled the tank with regular and didn't notice any problems with drivability and notice an immediate difference in the condition of the car from a cold start (no dips in rpm's, not stuttering and definetly no stalls) and everything has been golden. I noticed that when I ran regular on platinum plugs the car ran like trash (sluggish, not as responsive as with premium) but now that I've run the car on regular with run of the mill plugs the car runs like gold can anyone tell me if there is any correlation? .....BTW MY PROBLEM IS GONE!!!!!!!!!YIPEE!!!!!!!YIPEE!!!!!!!

 

On HowStuffWorks.com about octane and such, and I believe I read that too high of an octane can be just as bad as too low an octane. The car has a 'maximum' octane that it can use and anything below or above will cause a loss in performance. I don't remember exactly why, but I do remember reading that. That could be the reason. My SE runs on 93, but I might try going down to 89 because it seems like the 93 does no better than 93 the one time I could only afford 89 and so threw that in the tank.

 

It's always been my understanding that if you run a car for a long time on a specific octane, that if you deviate from that once the car has "got used to it" then it will run like crap. Example: go from 87 to 93, the car won't be able to burn the fuel and will run rich and poor. Just the same,go from 93 to 87 and the car will burn the gas up too quickly thus producing leaning of engine and a decrease in mpg becuase it needs more of the 87 fuel to maintain the same level of performance. Has to do with ecu and how it manages the performance of the vehicle based on the last 50 starts, etc. To drastically change the octane of fuel run in your car will make the engine run like crap untill the ecu can adapt to the new parameters. Like anything else, it also depends on the shape of the engine and the functionality of the ecu (we all know some like to play games with our cars!).

 

Are you using the wrong heat range spark plugs, or something like Bosch plugs?

 

Good point.