I'm new to Lexus, but I do have some automotive experience. I've noticed some hesitation or stumbling when accelerating from a stop, more when trying to accelerate faster. I pulled all the plugs, and the front three seem to look like they are running lean (white), while the back three are ok (brownish) plugs maybe had 20,000 miles on them. Things that I have done, replaced plugs Iridiums I had them out anyway, cleaned MAF and swapped with known good one, replaced VVT solenoids, replaced PVC and hose, used injector cleaner (three tanks of fuel). Also while cleaning injectors I checked the mileage hwy only getting about 16-17 mpg. It ran this way for about four month before the CEL with these codes ever came on. Any clues to what may be the problem. Thanks for any support .

 

I would try replacing the A/F sensor on the exhaust manifold for that bank. You caould always swap it with the other bank, reset the codes, and see if a code appears for the other bank. That would for sure tell you that the A/F sensor is bad.

 

Definitely that is your MAF Sensor

 

Both trouble codes and your spark plugs are pointing to the bank 1 A/F sensor. If you have a scan tool and know how to use it you can easily verify before replacing it. I don't think it is the MAF sensor. That would affect both banks.

 

Thanks for the feedback, I replaced the MAF sensor and found two sparkplug coils with cracks on the sides. I replaced all six coils and MAF with Denso parts. Now the only code that comes up is P0420. Now I looking for conditions that cause this error.

 

I usually got the 420 when either of my A/F sensors went bad; replaced the sensor and the 420 usually went away.