I had new plugs put in my Maxima a few weeks ago by mechanic #1 (not an official Nissan mechanic, but usually a good one). It was running good before then, but w/ 136,000 mi and original plugs, I thought it was time. Since then, it has not idled well and occasionally cuts off when in neutral at traffic lights (it is a 6-speed manual transmission). I took it to a different mechanic (#2 - NIssan dealer) yesterday, who told me that the air flow meter (mass air flow sensor, i think it is also called) was installed upside down. Is this something that would have needed to be uninstalled or moved to change all of the plugs? I’m just wondering if mechanic #1 messed up my car and should be responsible for some of my new bill from mechanic #2. THANKS!!!
I have never been under the hood of this car so I can’t say anything with any certainty. I’m mostly responding b/c no one else has so this will bump the question.
First, I doubt it is necessary to mess with the MAF to do the plugs. However, if this is a good mechanic perhaps s/he just pulled your intake to check it out as a courtesy (e.g. check for cracks, check air filter condition, etc. Frankly, if I were the mechanic and a “good” one and I knew you went 136K on one set of plugs, I’d take a gander at your air filter.
Second, I’m struggling with the plausibility of the MAF being upside down. For one thing, there are design issues - like the plug not reaching if it goes in upside down, or it not fitting into the intake. But I also can’t think of why it would matter in the least. Perhaps someone more experienced can shed light on that.
How much did you get charged by the Nissan dealer and for what? I’d imagine that there was diagnostic time involved but I certainly hope there was no arm or leg required to reorient the MAF.
Thanks for your response. I just got back from the Nissan dealership and a discussion w/ the Nissan certified mechanic who fixed my car. Turns out there were 3 issues: 1) an unclamped/unattached hose, left unattached by the spark plug culprits, 2) upside down and improperly attached MAF, 3) missing gasket on some hose attachment to the MAF. Per this mechanic, they always unhook the hose in 1) above and the MAF to get to the rear 3 spark plugs, so it was his belief that the spark plug replacement mechanic caused all of these issues, which were grossly affecting my air/fuel mixture. Cost at Nissan dealership was $162, which was all labor for diagnosis. They did not charge me for the replacement gasket and labor, which was very nice. So, I’m going back to the spark plug replacement folks tomorrow to discuss this issue and the whopping $368 bill I paid them for faulty work. 
I think that the dealer’s cost/action was reasonable.
The people at the shop where the plugs were replaced will likely want to know why you didn’t come back to them with the issue. Everyone makes mistakes. I used to paint (houses and stuff) - whenever I apologized to my boss for screwing up and making a mess of something he’d always say that the important part isn’t that you avoid making a mess. You will. The important part is how well you clean it up afterward. Wise man.
Smart man! Just to clarify, I didn’t go back to the original place because it is a 50 min. drive from my house, mostly interstate until you get a few miles from my house. On the way home, I didn’t notice the car acting strangely until sitting at traffic lights near my house. So when I drove it again, it died 4 times at different traffic lights, losing all power and steering at 35 mph, which is not good in heavy traffic. The Nissan place was an easy right turn at one of those traffic lights, and I’ve been there before for things, so feel they are trustworthy. I should have gone there to start w/ for the spark plugs, I suppose.
I hope they did more than plugs for $368. That’s a hefty bill to change 6 spark plugs!