unir2b1

This site has been very helpful...especially all the threads from LexMex. I just bought a '99 RX300 AWD w 80k miles from a local non-Lexus dealer. CEL was already on when I was test driving it but he assured me he would fix anything and everything, and thus far has been true to his word. They have now replaced all 3 O2 sensors and cleaned the MAF sensor. They have reset the system including disconnecting the battery and the CEL goes away for about 24 hrs then comes back on. I'm still getting codes P0171 (System Too Lean), P0136 (O2 Sensor Circuit), P1130 (A/F Sensor), and P1153 (Bank 2 Sensor 1 front manifold A/F).
Since all 3 sensors have been replaced and MAF has been cleaned and appears to be in good shape, the mechanic thinks there may be a probelm with the computer not recognizing 1 or more sensors. He's thinking of replacing the computer, which is fine with me because I'm not paying for it...however, does anyone have any other suggestions.
By the way, while I continue to drive it at slow speeds as my commuter car to work, the engine will sometimes start chugging if I keep it at one speed (40 mph) for an extended period of time...if I give just a little more or less gas the chugging stops. I've also notice that running idle at a stop light seems slightly sluggish like the air-to-fuel ratio is slightly off. I'm assuming this is all part of the same issue and that when sensors aren't working properly, it's going to effect how much fuel is being sent to the carb. Correct?
Any ideas would be much appreciated!

Lexmex

Well, what brand of sensors were used? In addition, I would also have the mechanic measure the resistance of each of the A/F sensors (this can be done with an advanced OBD2 scanner).

unir2b1

In addition to what I stated earlier, this morning I noticed that the transmission is not shifting into 4th gear. It's running 3000 rpm at 45 mph and 4000 rpm at 60 mph. Could this be related to my CEL issues and/or a bad computer?

Lexmex

Can you actually hear/sense the vehicle shift?

unir2b1

I can feel the first two shifts and visually see the tac go up and down, but then it does not shift into 4th when it is supposed to. Typically, I can cruise at 60 mph at 2000 rpm...this morning it was running 4000 rpm at that speed. And this was well after the engine was warmed-up.

Lexmex

I am trying to put this in my mind...

It appears if that is the case it is knocking you out of overdrive. Now that could be symptomatic of something else going bump, perhaps a knock sensor, even though not registering.

I am also wondering if perhaps there is vacuum leak somewhere on the system or bad injector.

I'd still have them measure the resistance they have on those 2 A/F sensors and I would like to know if they used Densos.

code58

What Lexmex said in the last paragraph is true- it may not be the problem but it is the first place I would look. Lexus are sometimes not fond of aftermarket sensors. Roger

code58

Make sure that they didn't put in O2 sensors. They are all commonly called O2 sensors but they changed, I believe in 1999, to a/f sensors and they are a very much different animal. Not being a Lexus dealer they might not know that and the aftermarket parts book often erroneously lists O2 instead of a/f sensors. They will not work! At least in Cal. they used a/f sensors in 1999 on Rx300's.
Hope this helps. Roger

yeuemhoai

iTrader: (1)

I recently got codes P0171 and P1130, cleaned the MAF, and cleared the codes by OBD tool but the Check Light and VSC came back.

My mechanic called the dealer and they recommended to replace both a/f ratio sensor (bank 1 sensor 1) and the post-cat O2 sensor. Please help if they are right.

Lexmex

Post Cat O2 sensor has nothing to do with that code. The P1130 is related to to exactly the bank 1 sensor 1 (A/F sensor behind the engine block). P0171 is an accompanying error and doesn't point to a part in particular.

lexus114

Just do the two a/f sensors,and you should be fine.From what I gather,the post cat sensor,doesnt usually give a problem.

TampRX300

The sensors are mixed up with O2 sensors if they replaced all three. Bad news for you. When I purchased my RX 3 weeks ago from a non lexus dealer, the very selling dealer sent it to Lexus of Tampa Bay because the don't allow their mechanics to work on BMW, Lexus and Mercedez. Mine wasn't shifting into 4/overdrive. Lexus replaced both knock sensors and that fixed the problem. Now I'm getting P1135 and P0125, that is the rear Air/Fuel Sensor that needs to be replaced. Part #89467-48011 or Denso 234-9009. Don't get it confused with the Post cat O2 sensor, they are different and cost abot $206.00 from the dealer, or Ebay for about $150 shipped. I'm ordering mine right now from Ebay, the A/F sensor Denso, new. That however, will not fix the knock sensor issue, those are more expensive.

TampRX300

They are right and you can save by doing it yourself, a ton! I did the same thing as you did, even cleaned the speed sensors on all four wheels to see if that took care of the TRAC OFF light that comes on at the same time, but the dealer told me that the TRAC OFF is following the CEL from the same code.

TampRX300

No offense to your mechanic or the mechanic, but if he thinks that the computer is bad and the car is still running, he is full of it. All you need is an OEM O2 sensor and 2 OEM A/F sensor. The chugging is being caused by the bad A/F mixture not only from the A/F metering sensors but is being aggravated by the O2 Sensors. The longer you drive it like that, you can kill the timing and damage the engine knock sensors, you can also "fry" or "kill" one or more Coil Packs. It's amazing how such an older (99') vehicle is still so unknown for mechanics that haven't studied it. Be careful, they don't know what they are doing with that car.

burteboy

I love this . Certain parts dont cut ends sensors are very important to the operation of your vehicle. Buy dealer item. i would like you to check behind your plenum there is a ground wire that screws on . its either loose or off, another the surface is dirty causing a poor ground. thats your problem.