2013 RX350 F Sport w. 105k miles. I'm the second owner and purchased about a year ago at 90k miles. It had an unremarkable carfax and proof of regular servicing at the local Lexus dealer. The car is visually in great condition and I swear even had some random whiffs of new car smell in 2023 buttttttttttt its getting funky on me. This is our 2nd one (previously a 2010) so I know it has some quirks (as all cars do). We are avid Toyota/Lexus family so I want to have faith its just normal car stuff, but even my husband who has been a mechanic for 15 years is questioning its reliability. Unfortunately, I was forced to purchase this in less than ideal circumstances (covid car market issues and I had a totaled 4Runner) so I overpaid by a couple grand. My hope was that it was in such good condition I'd keep it for another 50k miles and none of that would matter in the long run. It frustrates me to have negative equity in a car that might have expensive issues lurking around the corner. When the opportunity arose where I could dump it on a dealer, lose 4k, and get something new I am super tempted, but that feels like another short sided decision on top of an existing bad financial situation.

Anyways, video of the issue linked below. Twice now I have driven about 15 minutes in cold weather, turn the car off, and for about 2 minutes the car continues to run and theres a weird rattling/struggling sounds from the engine bay/outside of the car. It's as if the engine is still angrily working but the rest of the car is off. Maybe 2 minutes is an exaggeration but it was long enough to start making noise, allow me to make fun of the jeep next to me for sounding like ****, realize its my car, get my phone out of my purse, and record for 5 seconds.

I'm not confident any of its related, but for what its worth other quirks include: shuttering with light throttle noticeable while turning (roundabouts are the most obvious time) and is sluggish accelerating from a stoplight (randomly). Sluggish acceleration as in, you can mash the gas and there is far to long of a delay for the car to catch up to the input your foot is giving the throttle. There was one day where it turned on cold, blew burnt oil from exhaust, I drove it, spewed more oil a few more times then the check engine light came on, stayed on for an hour-ish, then went away and never came back. Fault code was a generic "startability fault" (P1604) not from the dealer but it was what we had available to us at the time.

Any opinions out there? We are going to do spark plugs, transmission fluid flush, and diff flush. We considered replacing the PCV valve. It feels unhelpful giving vague descriptions of random issues and I doubt its all related, but what would you do if you were in my shoes?

 

When you pull the plugs, do a compression test while they are out, can rule out lots of issues, and is cheap and easy while plugs out.

 

Have you checked for stored codes? If your husband was a mechanic he should be able to do all this stuff.

I would first try 2 bottles of Techron Fuel System Cleaner in the gas tank, one after the other on 2 successive tanks of gas. Get the 20 ounce bottles. Dieseling, which is what it is called when the engine continues to run on after being shut off is often caused by carbon build up. Techron will help remove it.
Then change your engine oil, check the air filter etc.