Hey guys so I've used this forum once before and I yet again am having another issues that I can't really seem to find a ton on. A little short history, car is a 2010 with 85k miles, one owner, doesn't get driven that frequently although has been more of late. Earlier this year(feb) had some rodents chew up the harness - nissan dealer replaced battery and harness, insurance covered it 100%. Was fine until around July when it was dead in the driveway after not using it for a weekend, no rodent damage or anything this time, had it towed to a non nissan dealer and they replaced the alternator and battery and it was fine again. Come to last week of October where I made a post on here saying I was driving around 30mph and the car just died with every dash light turning on, steering would not turn past 10/2 and had no power brakes/no engine power at all is how I would describe it, but all electronics including radio stayed on. Had it towed back to the dealer this time and they said it was once again rodent damage to the harness but not as bad this time they repaired it instead of buying a new one, and they said my ecm was fried, so they replaced it with a used one. Also I'm not a car person but was told a serpentine belt of some sort was installed backwards from the other shop on the alternator and it was almost destroyed?

It has been about a week since I've had the car back and it is doing some weird behaviors once again. I work from home so I only really drive it for groceries or other errands but since the first incident in Feb of this year I've been more diligent about driving it almost every day. The new issues I've noticed are that the car is loud, like very loud metallic whooshing noises when it's just idling, easily twice as loud as before this shop visit. Turning in and out of the driveway is also causing the power steering I assume? To for lack of a better word scream at me if I turn the steering wheel past a half turn either way. I've had power steering issues on a 97 maxima earlier in my life and this was significantly louder. The car is also putting out significant exhaust when starting and stopping, billowing amounts of white exhaust which I assume if you are burning oil the exhaust is typically black/dark with a smell correct?

The strangest thing it has been doing however, is this weird rpm ramp up and ramp down. I've been able to recreate some of it in an empty parking lot this evening, whenever braking to a stop, if the rpm goes below 1k it shoots up by about 5-600rpm and lunges almost? This is all while holding the brake and it is a visible jolting lunge. I made up my own test and from a stop, let go of the brake and on a completely flat level parking lot the car went up to 12mph gradually but rather quickly on its own without me touching the gas or brake at all and while running 1500~ rpm. It does a similar lunging rpm increase around 30-35mph sort of around the point it shifts into 3rd gear as well.

There is no check engine light on, there is no warning lights at all. I'm wondering if the replacement used ecm is bad or if theres some other significant issue the dealers shop didn't catch? I had a similar issue with my 97 maxima many years ago around 3rd gear not catching and causing the car to lunge which ended up in a transmission replacement, but if my memory serves this is a different feeling.

Like I said I'm not a car guy, all I know how to do is change a tire and add window washing fluid, and I don't know any other car people in my area. I'm essentially at the mercy of a shop or whatever I can find on the internet. Any advice would be greatly appreciated as this car is a bit of a family heirloom at this point and I would rather not sell/junk it and would rather be prepared with some knowledge before I call the shop again tomorrow. Thank you.