Our 2007 G35 sedan has started having problems with steady state surging. Initially this started with hesitation from a stop and then it developed the surging at low speed. It seems to occur when the engine is still cold, but not when it is hot. I went through the accelerator release position learning and throttle valve learning (although I'm not sure I performed this correctly at the time) first and this did not help. I checked the battery and voltage was only 12.4 and it was the original battery so I replaced it. First drive away from Autozone nothing felt any different. Hesitation was still there, but after driving it for a while this went away and the car felt like it did when we first bought it. My wife drove it the next day and said it drove well now. Couple of days later and she tells me the surging is back and now it occurred at 45mph. I have not had an opportunity to check anything or drive it myself, but I'll get to this weekend. Anyone experienced this?

See if the alternator is charging at 14.5v +/- when the engine is running. Otherwise I would look at something else causing the surging...fuel/spark/air. If you are up to date on spark plugs then look at fuel/air. With it seemingly going away when warm it may be the MAF.

Audtatious, I just checked battery and charging system. Battery is 12.6vdc but charging started at 13.6 and dropped to 13.3 so it looks like I have a bad alternator/regulator.

I went through the charging system portion of the manual and it says the voltage from the alternator should be 12 - 13.6vdc at 40% load. Although I don't have a charging load station, with the lights on and AC on (pretty much full load) I have 13.18vdc at the battery. Car off voltage is 12.58vdc. To me it looks like the charging system is fine per the manual. Now, compared to my Saab 9000 (car off voltage 12.6, engine running 14.6vdc) it sucks, but it appears this system output is supposed to be lower.

I replaced the battery on my coupe Thursday and the alternator immediately was charging at 14.56v. I had the alternator of our G35s sedan go out at 100k miles (no alternator issue with the G37 yet, but this is my second battery replacement)

I'll have to get it checked then to make sure. Did you replace the alternator with one from the dealer or aftermarket?

Update: got an alternator at Napa yesterday and installed it yesterday/today. After starting it up I checked the output and still got 13.288vdc. Drove to Napa to return the core and also had them do a check and their meter showed 14.2 even under load. I should've checked with my meter at the same time to confirm as when I checked at home I still got 13.28. The car drove well though and other than slight surging just as I was going through my parking lot there was no hesitation and it drove smoothly. I also noticed the neutral/park idle was down from 800 to 650rpm.

Test your meter with a new 1.5v battery

Been away from the forums awhile. I tested my meter and it is good. I think the issue is the way this charging system works. If I'm not mistaken it only boosts the alternator output when the load requires it. This would explain why I would initially get 13.7 then see it drop to 13.2. Anyway, I'm still troubleshooting this when I have time. It's not undriveable and the hesitation/surging only occurs during a certain period of time when the engine temp is in a just warmed range. The saga continues.