I have a 2007 Lexus IS250 with 106k miles that is misfiring, having loss of power, rpms dropping and shaking at idle stop lights, and it seems to be worse once the engine has warmed up. It had no check engine light at all for a few days and then when going up a hill i lost a ton of power and got a flashing check engine light. my OBD2 said it was a Pending Cylinder 3 Misfire, and when i started it the next day the check engine light was gone like before and like before was still misfiring with same symptoms.

I had a a check engine light and a Cylinder 3 Misfire about 4 months ago and changed all the spark plugs and the one coil for cylinder 3 and it was fixed and drove great after that.

I took it to my local mechanic and he said it was also sometimes misfiring on Cylinders 1,3,5 (the 3 on the left side) and he thinks one of the catalytic converters on that side is gone bad or clogged or something and to take it to a muffler shop (planning on doing).

On my way home from the mechanic i got a flashing check engine light. i was surprised bc it was such a short drive on flat ground unlike the hill where it happened before. I got home and checked and it was another Cylinder 3 Misfire but this time i got a solid check engine light when i turned the car back on. i ran some Cataclean through it but did nothing.

I am unfortunately not a man of means and already spent $300 just to get it semi “diagnosed” by my mechanic and im sure the muffler shop is gonna cost something similar to do the same. I would hate to spend 1k-2k on new cats and it not be the issue.

Has this happened to any of you? Is this carbon build up? Should i get it walnut blasted? Is it really the cats? I really dont know a ton mechanically but know the basics so i dont really know what to do and really dont want to spend a bunch of money i dont have getting it fixed and not actually fix the issue.
I bought this car bc ive always wanted one and have only heard great things about its reliability and them getting to such high miles so this is a bit upsetting given that i only got the car 7k miles ago

ANY HELP GREATLY APPRECIATED THANKS!

 

When was coolant changed last time? Do research how to check coolant leakage and how to check if head gasket is leaking.

 

Turns out it was just a faulty coil. #3 to be exact. it was an aftermarket coil pack i bought when i got a misfire on #3 cylinder around 4 or so months ago when i changed all my spark plugs. i decided to just buy one coil pack for that one cylinder #3 bc the OBD2 said it was a cylinder #3 misfire.

i guess after market products really dont go well with these cars bc when i changed those spark plugs and one coil pack i bough just regular iridium spark plugs with the correct gap and everything bc online everywhere people said thats totally fine. but it wasnt and it made it worse putting those plugs in.
so i ended up going all the way to my closest lexus dealer and getting the exact Denso spark plugs that come factory and they worked perfect immediately. so ig its OEM or nothing with these engines lol