Rpm dropping and going back up and down with light acceleration?

I don’t see video in my question, so here is the video:

Thanks for the video, it helps. so, the p0420 code is the clue.

The P0420 code for a 2014 Nissan Sentra indicates a problem with the catalyst system efficiency for Bank 1.

What happens is the catalytic converter breaks apart and clogged the exhaust system outlets. Which sounds like what happened to you. The cat is a part of the exhaust manifold so the unit will need to be replaced if confirmed bad. This guide can help, and I have included images in the diagrams below for your car.

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

and

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

I would take a rubber mallet and tap the exhaust system to see if you can hear something loose which is a sign the cat is the problem, check out the images (below). Let us know how it goes.

Thank you for your reply, I don’t have a rubber mallet but I'm not sure what part you are talking about. I took a picture under my hood, I knocked on the yellow circled part (no noises or rattles) but let me know if this is the wrong area, please. I will say I noticed that the tube going into my air filter (circled in blue) is really loose as it goes down into my driver's side fender well (i can pull the tubes out from each other easily), the plastic itself is also incredibly loose and can be moved with my hand. not my air filter as its new and clean. Thank you!

I am sorry I meant the exhaust system under the car. Here is what it looks like. Check out the images (below). Please let us know what happens.

Hey! So I did some tapping. (Sorry for the late response, work and school is ramping up) No rattling or anything along those lines. I had the emissions tested and that’s fine too, my car runs naturally like this with the light on I assume. On the hand, I’ve had some mechanic buddies of mine look at! Here’s what we found: I’m missing a bolt right near my air intake manifold system, and with that, it’s incredibly loose. Also, if you place your hand under the 2nd to the left part, cold air is flowing in or coming out (yellow arrow, underside not top view). I’ve also noticed that the problem is way worse in cold weather and warm weather it does just fine.

Here’s the image, the yellow arrow is where we can feel the cold air. Don’t know if that’s normal but in case it helps!

No worries, can you hear a whistle noise, a vacuum leak? I have seen the intake manifolds crack and cause an engine vacuum leak. This guide may be able to help you confirm the issue:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please go over this guide and get back to us.

Yes actually but it’s not consistent meaning it doesn’t happen when the car is just on and running. In the original video I posted, it may be audible, but I doubt it. Anyways, while it jumps up to ~2000 RPMs it makes a woosh sound like air is being sucked out. Only for that second that it’s stuttering, if I leave it alone and stay under ~1750 it won’t make the sound, it won’t have the jumping + sound issue if i just go ahead and press harder on gas. Also, as it’s gotten warmer haven’t heard the sound as much as when it was 22 degrees F, we had a 50–60-degree week where it barely did give me any issues. back down to 40s now and she’s not liking that.

I will definitely grab some carb cleaner and try it out!! And let you know the results. Just scared it could be the terrible CTV but with the woosh noise I doubt it.

Yes, I have seen the CVT make all kinds of weird noise, so does it make the noise when the transmission is in park and you rev the engine?

No! No sound at all, and I don’t have the loss or stutter of power either. No knocking. It’s really on when I am actually driving. It runs louder but not in park either. trans in it is relatively new and was replaced at 100,000 miles, just barely has 26,000 on the new CVT but I have a transmission fluid drain and replace coming up.

Yep, I would try that first to see if it makes a difference, did they install a new, rebuilt or used transmission?

It was new from the Nissan dealership; a private dealer bought it from the dealership and that’s where I bought it from.

It should be okay then unless you got a defective unit. Let me know what happens after the service.

Hey! So good news and bad news. I ended up needing the transmission replaced, but it was covered by warranty. That said, I just got my car back this Monday, this same week (Saturday) it’s doing the rpm dropping and making the sound (but the entire duration of stuttering) again. only 400 miles on it :(

Hmm, so it is back to the same problem? If so I am wondering if the dealership is doing the repair correctly, do you have another dealer near you the car can be looked at ? Can I get a short video of the noise?

Essentially, I just had my CVT trans replaced literally this week from a Nissan dealer. Got it back on Monday and it is currently the same week on Saturday. 400 miles within that one week. Now, my car is starting to exhibit the same problem before the cvt failed… I accelerate, get the car to 2,000 rpms, and it doesn’t want to go higher than that. I get a squeally spinning noise and it flutters in between 2000-1500 until i either let it off the gas (which stops the noise) or press harder on the gas, also stopping the noise. Like I said, only 400 miles and just replaced. At this point Im at a loss, im attaching the video in the reply of what its doing.

Here’s the video! Only note is that this video was from before I got the new transmission put in. But, it’s the same symptom. Only difference is that the wooshing/spinning noise in the video (very quiet) is lasting the entire duration of rpm’s fluttering and not just the one time.

Sorry, that was just a screen shot, actual video is here lol.

yes and no to the exact same problem. It’s not surging as hard, but the noise was more consistent. I’ve been driving it today compared to having the fluke yesterday and it’s been fine. It hasn’t happened since. I’m just monitoring it right now, but it was the same kind of symptoms. I still have it under warrantee so I am calling the shop, but I really want to doubt that it’s going to give me trouble with only 420 miles.

Thanks for the video, yep that is not normal and the slight noise it is making is not good either, also I noticed the check engine light on so we should run the codes to see if any are for the transmission which can further the diagnosis. Here is what I would do first:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

They will read the codes for you at AutoZone, then get back to me so we can figure out what to do. To me it sounds like the transmission is defective but let's get the codes first.