loofaunce

As the title says im trying to help fix my moms rx300. Its a 1999 rx300, not sure what submodel if applicable. Its got a v6 in it with some oil leaks (im fairly certain its the valve cover but that doesnt look like a fun job), the speedo doesn't work normally, sometimes it does but it wont show any over 30mph.

the main problem is one of the coils keeps going bad, I think its #4 but im not certain (its the one viewable from the front of the engine bay in the center if that helps). We replaced it twice and it went bad twice. Im a bit of a noob when it comes to coils as ive only ever dealt with regular spark plugs.

Would appreciate any info or suggestions. Feel free to educate me 🫡
I am relatively educated on older toyotas as I have an 88 corolla project and 97 celica daily but dont know much abt lexus tho i assume theyre probably similar

MattRX

What brand of coil did you put? The 1MZ is really picky for coils and sensors in general, it doesn’t really like anything other than Denso. Even members on the Highlander group have had trouble with Bosch etc. I’d throw in one Denso and some NGK plugs

If doing valve cover gaskets, I’d do PCV valve too but I’d swap to the rear 2005+ 3MZ-FE cover with revised metal PCV valve and oil baffles. Brought an end to my oil burning once and for all

If I could go back, I’d do my gaskets all OEM as the price difference wasn’t much and the OEM gaskets fit better, especially the spark plug tube seals

https://www.toyotanation.com/threads...#post-14842478

maxSteel

These are just normal spark plugs with each having its own coil. Next time one appears to fail swap it with the adjacent one to see if the problem follows. As MattRX advised, use Denso (bought from a reputable seller).
As for the speedo, do you have any engine codes? Is the ABS light on?