2017 Corolla iM idle fluctuation ; Rev sound ; Weird vibration

#1
Hey guys, just bought a used Corolla iM this past weekend and having a few issues I wanted to see if you all had seen!

1st - At idle it stays at 1k rpm for most of the time but every like 10 seconds there's a 3-5 second period where the car drops to 500 rpm. Then it hops back up to 1k rpm. When it drops to the 500 mark it start shaking like when you're in a manual and you aren't gassing it enough in first and it shudders. Not quite as bad but like that. A mechanic I called said maybe the airflow is having an issue and/or the throttle body needs to be cleaned.

2nd - When I throw it in neutral and rev the engine up hard it sounds like a bad alternator I've heard before. Really loud whine on top of the engine sound revving.

3rd - You know when you have a flat tire that you're driving on and it's that constant thump in intervals as the tire rotates that you can hear and feel? So replace that with a vibration. Not something that shakes the whole car but I can feel it in the pedals pretty well and hear it pretty clearly. Almost like when you're driving on a crappy road if that makes sense.

Any ideas hopefully? I read one article for another corolla earlier when I was looking and some people were saying that's normal but the fact it's shaking is a bit bothersome. Thankfully I have the warranty through CarMax where I picked her up so they're going to cover anything since I LITERALLY BOUGHT IT THIS WEEKEND. Thanks a ton for the help in advance and I hope to get to know some people here and learn some stuff!

2017 Corolla iM
30k Miles
CVT Trans
No mods (yet)
 
#3
1. Clean your throttle body and MAF sensor. Inspect your air filter.
2. Possible serpentine belt, belt tensioner, and/or idler pulley
3. Tires worn/out of balance?
Yeah that's exactly what my mechanic told me when I called for an opinion lol. I'm going to bring up the the TB and the MAF when I get it to CarMax Friday and see if they actually do it.

That exact thing came to mind 2 nights ago when I tested it again lol. It started doing it worse this morning on the way to work so i'm curious on if I'm about to pop a belt soon.

Balance would make sense, but the car drives perfect and doesn't sway if I'm not holding the wheel. Plus the tires I think are all brand new on the car.
 
#4
If it's still under warranty, have them recheck the tire balance. Did you test drive, prior to purchase? Sounds like you inherited someone else's problems. Good luck.
 
#5
If it's still under warranty, have them recheck the tire balance. Did you test drive, prior to purchase? Sounds like you inherited someone else's problems. Good luck.
Yeah, the test drive went perfect and it drove really well for a couple days and then started doing all of this. It feels like whoever drove this car drove it ragged and then traded in, that or I'm just stupid unlucky with this purchase. I want to keep the car but technically I could return it by saturday and I'm going to have them extend that because of all of this to give me more time to think on it.
 
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