@monju0525 You are absolutely right. I am on the third set of spark plugs. Replaced at 60K intervals.

 

U did everything by the book. No criticism here.

 

HD is the new RockAuto

 

looks like 6731311 is what you need.

 

I used the BlueDriver Bluetooth Pro OBDII Scan Tool, which only showed a P1605 code but didn’t provide any specific cylinder misfire codes like P0301, P0302, P0303, etc.

That’s why I ended up going to the dealer for a full diagnostic.

What diagnostic tool does the community recommend for Lexus vehicles?

 

I dont know about HD, some folks caution against buying auto parts from HD, Amazon and E-bay.

Also HD did not carry DENSO 6731311, so i ordered a coil from Rock Auto!

Thank you all for your help.

 

You deserve a special thanks for these pictures!

 

I replaced the ignition coil and took the car for a test drive. The previous hesitation at 25–30 mph is gone. At a steady 50 mph on the highway, I felt slight jerks. I later noticed mild hesitation at new speeds—around 18–20 mph and 30–35 mph.

After clearing and rescanning the codes with my OBD scanner, P1605 (engine knock) and B15EC (telematics) reappeared. The engine no longer makes clunking noises, but while parking, the tachometer needle pulsed slightly—less than before.

Any suggestions?

 

I think the jerks you are feeling are transmission related, "normal", and covered in other threads here. Can't make anything of slightly pulsing tach, would need more to diagnose.
The telematics code can be ignored. The knock code I would keep my eye on see if you get any other ones. I would try cleaning the MAF, throttle body, check vacuum hoses visually and listen for leaks, get charging system (battery/alt) tested at auto parts store. Doesn't really sound like there is anything wrong but a failing battery/alt can cause strange electrical issues, and cleaning the maf and tb are appropriate at this mileage it can't hurt.

 

TY! These items - I would try cleaning the MAF, throttle body, check vacuum hoses visually and listen for leaks - are these DIY or best done by a mechanic? And what would be an estimated cost to get these items done at a local mechanic (not a dealer).

Also - a new battery (AGM) was installed 3 months ago.

 

Likely was not ever the coil pack. If it was, it should've 100% thrown a flashing CEL. How does the car run on cold start? If you start it first thing in the morning and run it up to the problem speeds, does it have issues? How about when you're hard on the gas? I did a quick search on the code because it intrigued me and almost all the problems I saw with Toyotas was the fuel pump or the fuel pump control module. My initial guess would've been bad gas but it's been a while, you should've run through a tank by now.

 

Your initial guess would have been a bad guess, or bad gas?

 

Gas. Fixed, thanks for catching that!

 

My car has always started without issues when cold. However, after driving on the highway and transitioning to city driving, I began noticing hesitation when accelerating from a stop—particularly between 25 to 30 mph. This was the first noticeable symptom.



On a couple of occasions, I also detected a gasoline smell inside the cabin, although this has not recurred recently.



Another issue was a pulsing tachometer after about 20 minutes of driving, typically while idling at a red light with the engine running. Occasionally, I also heard clunking noises from the engine under similar conditions—again, only after the car had been running for a while.



Notably, none of these problems have occurred during cold starts.



Based on my research, I initially suspected a faulty fuel pump and found that Lexus had issued a warranty extension (CSP 23TE01) for a related issue. I brought the car to one Lexus dealership, but they didn’t find any problems and stated it was extremely rare for a Lexus to exhibit fuel pump-related symptoms.

• CSP 23TE01 Service Bulletin (NHTSA)
  
• Toyota Pressroom Recall Notice
  

A second dealership diagnosed a failing ignition coil, which was replaced with an OEM part. That resolved about 80% of the issue, although I still experience occasional hesitation—particularly when accelerating or driving at higher speeds (55–60 mph).



I recently had the MAF sensor and throttle body cleaned, which noticeably improved throttle response. The hesitation is now less frequent but still present.



I plan to drive the car for another week to see if the ECU will adapt and eliminate the remaining hesitation. If the problem persists, I’m not sure what the next step should be. I always get top tier 87 Octane gas from Costco.



Any thoughts or suggestions would be appreciated.

 

It seems like it's just had a parts cannon blasted at it. If it were my car I'd find someone who is a diagnostic mechanic watch the ECU parameters while I produce the issue. If it's a fuel pump issue you should easily see it in fuel trims or commanded vs actual fuel rail pressures