shark13

Hello,
I've been reading through several posts trying to get a sense of what may be going on in my car but I wanted to get a few more opinions if possible before I started down a path.

Rough Idle: My 99 RX300 has been idling a little rougher over the last month or so. When looking at the engine you can see a slight amount of more vibration than normal, but where it is more obvious is at the exhaust. The flow of exhaust is irregular. Not real bad "put" "put" sound but noticeable. Recently with the AC on the rough idle was noticeable even in the card.

Hesitation: Here and there in the morning when I drive uphill the car would accelerate very slowly...almost struggling to get more speed. I don't think it's the tranny because it's only 4 years old (replaced) and when I push on the peddle the engine didn't rev up...it just very slowly increased it speed...even if the pedal was to the floor. Eventually it seems to work through it and the power returns. This only happens in the morning.

I am getting two codes. One is P0125 and the other is P1135.

I have cleaned the MAF sensor, the IACV, and the PCV valve.

Any thoughts?

Baetke

Is your check engine light on steady or flashing?
It sounds like it might be running in "limp" mode.

carguy07

A/F Sensor B1S1, buy only Denso. As Baetke said, you are in limp mode.

hypervish

I'm fairly certain that an A/F sensor fault code will NOT set the car into limp mode. Something else is causing the power loss.

timmui

Seeing that I am seeing multiple threads on this, here is a link:

https://www.clublexus.com/forums/rx-...5-codes-3.html

I do believe that a faulty A/F will cause something akin to limp mode. Waiting on OP to confirm if his CEL is flashing.

carguy07

I have been in limp mode many times from a faulty A/F sensor.

More than I care to recall. Almost ready to put a few on the shelf so I have them "in stock".

shark13

Thanks everyone for the great number of responses. The engine light I am getting is not blinking (thankfully). The suggestions above (replacing oxygen sensor) was the route I was considering as well. My first thought was to double check the resistance on the sensor as some have done.

I have read elsewhere that the P0125 code can be associated with the P1135 code and that once the sensor issue is resolved, both problems will be resolved. Anyone else agree with this assessment?

Can someone confirm again the Denso part number for the oxygen sensor. Does this most likely point to the O2 sensor located towards the firewall or could it be the one located near the front of the car? Is the same part number used for each of these sensors or do they have different part numbers?

artbuc

You can bet the farm on it. P0125 is a companion code with A/F DTC's virtually 100% of the time.

hypervish

Interesting... I stand corrected!

shark13

Just to confirm a few things.

I've heard the terms A/F sensor and Oxygen sensor used it seems interchangeably. Are these two descriptions of the same thing?

If indeed what I need to replace is the Oxygen sensor, does it sound like I will need to replace the sensor located by the firewall?

carguy07

You need the A/F sensor by the firewall. A/F sensor is a fancy O2 sensor (wideband?). The A/F sensors on this car are in the exhaust manifolds (screw in). The O2 sensor is down by the cat and is a bolt on.

kalali

You must have something (else) causing frequent A/F failures if this is all in the RX.Those should last almost the life of the car or at least 100K miles.

carguy07

True on most cars, but these ones seem to eat them regularly.

hypervish

I don't want to take this thread off topic, but these car's do not eat them regularly.

Replaced B1S1 at 85,946. Still rocking same sensor at 208,000 miles.

Replaced B2S1 at 150,000. Still rocking same sensor at 208,000 miles.

Replaced B1S2 at 158,700. Still rocking same sensor at 208,000 miles.

Pretty normal to me. All sensors were original before I replaced them.

kalali

My record is even better. I've only replaced one at 125K miles - the one near the firewall. All others are still originals after 174K miles.