akonful

I have a 2015 Lexus RC 350 F sport. I have had it for 3 years now with no major problems. One day I was on the highway and the check engine light came on and I noticed the engine was knocking when I would press the gas. Its like the car wasn't getting power. The tracc off symbol came on eventually as well after a few shut offs and on's. I took it to the shop and they read the code. Said I needed a tune up. They replaced the spark plugs/coils. I get on the highway about a week after and within an hour the engine light comes back on and the car wasn't getting power to it. Took it back to them and they said the code was a cylinder misfire. They checked the spark plugs and said they are good. Took it on the highway again and light came on again. This is very frustrating since I have had no issues with the car up until now. Its like when I hit high speeds for a while now the car eventually loses power and the light turns back on. This is very frustrating because the shop is lost too so that doesn't give me confidence that this will be fixed. Anyone had this issue?

Forewheel

So I had this same issue minus the loss of power, but turns out, after a TON of research, I literally went out and tightened the gas cap and it went away....instantly. You have to make sure the cap does the 'click' sound. Not sure about the knocking and loss of power or what not you experienced but that fixed it for me, and is a common issue with Lexus cars in general. Hope this might help.

CharlieRC

Loose fuel caps have been an issue with error codes for years on all electronically controlled vehicles, not just Lexus. This sounds like a little more than that with the initial post.

Forewheel

I guess the part where OP said "it needed a tune up" was what cue'd me to a simple fix. Shops are always looking for a reason to make money.

CharlieRC

If you don't trust your car mechanic, find another one. Mine, I've known for over 30 years, worked on everything I've owned, (a lot of vehicles as well)
He is also a friend, this also helps.

Forewheel

Not sure if you're backing up my statement or not, but i've not had to use a mechanic for issues with my car since it's been bomb proof. .....other than the fuel cap.

Happy New Year Y'all!!

CharlieRC

I'm agreeing with you. I was just stating that I think there is more to his issue than a loose cap.
My 2015 RC is trouble free as well, as all other Lexus cars I've had in the past. (4)
I was merely stating that it's not been the only brand of car I've had over the years.
My mechanic is top notch, but has not even touched my RC, no need. Why fix what's
not broken.

15RC350F

I echo this exact statement!

Forewheel

So....update here. I think my fuel cap is broken. All was good, then fueled up again today. Made sure it "clicked"...then about 5 miles later it lit up and all the glory of dash lights is back on. I was messing with it earlier and the cap does the click sound, then about 2 seconds later talks back with another "click". It just won't stay in place. Going to order another fuel cap but i'm 100% certain the cap is the issue here. Only 28K miles on the car but it IS coming up on being 7 years old so........

Giangsturh

just a dumb question here, if the fuel cap was never " tightened " after 2-3 clicks, wouldn't the dashboard indicate that the fuel cap is loose?

Forewheel

Apparently not.....it triggers traction control warning, CEL, and cruise control doesn't work...and who else knows. But yes, you would think so, unless i'm missing something myself. All I know is the current cap on my car will not stay "clicked" in place. New cap should be arriving sometime today.

greasefin

If the gas cap is not tight then the gasoline vapor recovery system, the charcoal canister, is not recovering gasoline vapors in the headspace above the liquid level of the gas tank. This is an emissions issue and should always trigger a fault code but never alter the performance of the engine that one could feel. In my experience, a faulty fuel injector or a faulty spark plug may cause this problem but is rare.