Im surprised they'd try to lay blame on the oil versus the intake first...anytime you muck with the MAF you might be in for trouble...

Cylinder misfire
 

I had a SES light come up a few months back. The tech had to talk to someone at the factory because he couldn't figure out why it was a code for a misfire. My car is a manual w/ sport package and no mods (just AMSOIL). He said only one other 370 has come in with this misfire and from what we could figure it was from tagging the rev limiter. It made sense because I do stretch her out from time to time. One thing I remember was that the idle settled @1,000 rpm with the SES light on and went back to its normal 650 rpm idle after the code was cleared. I've put about 1,500 miles on the car since the code was cleared and have been trying to shift right when I see the light come on. So far so good. I don't think Royal Purple would hurt your engines' top end, but if you want a synthetic with esters AMSOIL and Redline might be worth a look. BTW I have @ 11,000 miles on my Z.

***UPDATE****
Just talked to the tech again

They are saying the oil and Carbon deposits on the throttle body are causing the P0305 SES light.

They want to do a fuel service cleaning, don't think I am saying it right but they say that it is done about every 15000 miles. Is this true and should I get it done.

They also want to replace the passenger side cabin filter and do the flush but its expensive like 175... Is it worth it?

I have had the SES light come on four times since i got the car in Nov. The first was at 80 miles on the odometer, random misfire (P0300), and i just had it cleared thinking it was a fluke. The second time (80 miles later) took it into the dealer, they dismissed it saying it was working the "kinks" out of the system or something. Didnt really believe it, but thought maybe some fresh gas (the tank was full when i test drove it) would help. It was about 1500 miles later and came on again, the dealer did an idle air relearn procedure. Then about 400 miles later it came back on. This time they kept it for two days, and working with Nissan Tech support they replaced both MAF sensors. They had noted that it had been running rich, and this had taken care of that, and I believe that will actually solve the issue.

Everytime the light came on as a random misfire (P0300) and it was after the car had sat overnight or all day will I was at work (8+ hours) and came on during the initial startup. Only time will tell if this really takes care of it, I have about 400 miles on the car since the MAF sensors were replaced, but I feel more confident since they actually replaced something rather than just resetting the ECU, and that it took care of the running rich condition as well.

I dont know if something like that could trigger a specific cylinder misfire, although if it is related to the MAF sensors, they intakes would be a very easy scapegoat.

Simple deduction says that the intake is filling the other two cylinders on that bank just fine with air, therefore there's no reason it would omit filling the misfiring cylinder with air...

Intake has nothing to do with a single cylinder misfiring. I'd wager it's the coil on plug for that cylinder or the controller or a plugged injector.

I wonder when they'll say you have to use Nissan Brand Gasoline?

Total BS. Contact Nissan and tell them the dealership is screwing with you. That or take it to another dealer.

All Nissan dealerships LOVE warranty work. There is nothing in the service manual that states that one needs a fuel service cleaning every 15K.

The throttle body has nothing to do with a misfiring cylinder.

:facepalm:

If it's under warranty tell them to fix it by whatever means they have at their disposal/cost. Or, go to another dealer for a second opinion. You can do without the cabin filter for $175.

From what I found months ago, Royal Purple is indeed an ester based oil. That is why I decided to use it in my 370Z and have been for 7500 miles without issue. 2 track days and lots of daily abuse. I doubt the type of oil you used was the issue.

Semi-off topic but I thought I'd throw it out there. For maintenance, or to correct MAF deposits from an over oiled (oil based) filter (like what they may use on aftermarket intakes) there is this stuff:

CRC Mass Air Flow Sensor Cleaner:
http://www.crcindustries.com/catalog...sers/05110.jpg
The guys on the M3 forums who had some higher mileage cars reported noticing a difference after cleaning FWIW. Maybe it's something to consider after you service your filters to avoid possible codes later?? Again just thought I'd throw it out there.

anyone else use this:
http://www.stp.eu/uk/images/product_...ioncleaner.jpg

every 6-7k miles?

And really? Carbon deposits on the throttle body? The one thats always open seeing as our valves themselves are the throttle body?

That's my point.

Carbon will never deposit on a throttle body...ever...(OK, exceptions: if you have blown valves and are backfiring through the intake or a really bad crankcase blowby issue with smoke billowing out your PVC hose, even then that'd be more like smoked oil/soot deposits not carbon build up)

Have them change your tailight fluid and muffler bearings while they're at it.

On an old 240SX I had there was some build up around the throttle plate that was affecting idle. It was more like dirt though, not sure how they are calling it carbon...

go buy a can of BG 44k, that should clearn ur engine up