Blueskies1

Hello everyone! I recently purchased a 2002 Lexus ES300 with 193,000 miles and have run into a few problems for which I could sure use some help.I apologize in advance for the long post, but I came across this forum and tried looking up my codes/symptoms but nothing matched perfectly, so I thought I would ask for your collective help.

Approximately a week after purchasing it, the check engine light came on. During this week of driving (about 15 miles to and from work, mixed city/highway driving), I noticed that when the engine is cold, it drives perfectly fine. Once warmed up, there is a moderate hesitation from 1500-4000 RPM. I also noticed that sometimes it doesn't shift into 5th gear on the highway and that if I clear the codes, it will shift into 5th perfectly fine. Also, after clearing the codes, the hesitation improves (much less pronounced), but gradually comes back and gets worse. There are no problems with idling.

I have an OBDII scanner and codes P0440, P0441, P0446 and P0325 showed. I researched on here and found that one of the more common causes for the P0440, P0441 and P0446 codes is unplugged/missing vacuum lines to the airbox. When I looked under the hood, the T-shaped vacuum line which connects from the purge valve to the airbox was missing. Also, the two vacuum lines which come from under the battery were both unplugged (to my understanding one connects directly to the front of the airbox and one perpendicular to the missing T vacuum line). I purchased vacuum lines and T-connector and reconnected everything.

For code P0325, to my understanding the knock sensor for bank 1 needs to be replaced. I purchased everything, including some "while you're in there items," such as: OEM Lexus knock sensors (2), knock sensor wire harness, water bypass hose, spark plugs, valve cover gaskets, plenum gasket and intake manifold gaskets. I plan to do the work myself this weekend, based on the DIY tutorials on here.

After reconnecting the vacuum lines, I reset the codes, however after about 100 miles of driving, the CEL comes back on with the same codes. I understand that there are multiple reasons for these codes (purge valve, gas cap (which appears to be new), charcoal canister, etc.).

I took the car to a mechanic and to have him diagnose the hesitation and codes. He said he cleared the codes and the car drove fine with no hesitation. When I explained that I had also done this and the hesitation and codes will comes back, he said the charcoal canister may be to blame, but I can try cleaning the MAF first.

I wanted to know if:

1. How could I help narrow down which component(s) are causing the P0440, P0441, P0446 codes, rather than start throwing parts at it.
2. Could any of these codes be causing cause the hesitation?

I live in New Jersey and need to have the car inspected soon, so the underlying problem needs to get resolved. Any input would be appreciated.

LeX2K

I suggest fixing the knock sensors before diving into the evap problem. No overdrive (5th gear) is because there are codes set computer disables O/D. Replace the gas cap gasket (77316-33042) or the entire cap (77300-47010) that will probably get rid of at least one of your codes.

Blueskies1

Yeah, I'm planning on doing it this weekend. I'm hoping it will resolve the hesitation as it becomes very annoying to drive.

Blueskies1

As an update, this past weekend I replaced both the knock sensors and the wiring harness (both purchased from Lexus, and came wrapped in Toyota packaging). After driving it afterwards, the hesitation was improved but still present. While taking everything apart for the knock sensors, I noticed the intake boot/hose was cracked and attributed the remaining hesitation to that. I ordered the boots (both of them) and they should arrive today, however on my drive to work today the hesitation worsened (just like it was before) and the CEL came on. My scanner indicated P0325 again! How could this be? I used OEM parts for the both sensors and the harness. Any ideas?

Arsenii

Hello,

To see if it is indeed a sensor at fault, use your old wiring, or the wiring out of any old A/F sensor to make an adapter that would swap the Sensor Signals around, feeding Bank 1 signal into Bank 2 and vice-versa, here is a thread on how to de-pin a connector. When done, see if you will get a different code for the Opposite Bank, if so, the issue is with the sensor, if not, the issue is on the ECU side or the wiring.

For how praised OEM parts are, Knock Sensors seem, or at least seemed for a little while to become outliers and a source of some major headaches for manufacturers, as they tend to be quite fragile, even Genuine parts won't guarantee you a working sensor. Toyota does provide a warranty on their parts, but it's about the worst on the lot, every dealership has their own policies, and usually unless it's the dealership that did the repair, you will be denied the coverage.

Hope this helps and best of luck!