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Discussion Starter #1 (Edited)
Hello all, I'm new to Toyota so bear with me if I get some things wrong here.

I am working on a 2001 Camry LE V6 3.0 and the vehicle suddenly began to stutter and stall at stop lights. Eventually it died and I was unable to restart it, so it was pushed into a nearby parking lot and left overnight. Came back the next day and it fired right up. Drove it around a good 15 minutes and nothing happened. Finally I parked and idled, nothing happened for a while but eventually the car struggled and hesitated, RPM's going below 300, and it almost stalled. But it didn't stall. It only did this two times in the span of 5 minutes and then didn't happen again while I idled for another 10 minutes.

Using the OBDII app I was able to see that there were some wild fluctuations in the Short Term Fuel Trim and that I wasn't able to read values from all oxygen sensors. As I understand it, the V6's have 2 upstream and 2 A/F sensors. Here is all oxygen sensor data I could read with my OBDII tool:

Bank 1 Sensor 1: ---
Bank 1 Sensor 2: 0.005V or 0.889V
Bank 2 Sensor 1: ---
Bank 2 Sensor 2: ---

I also had an "O2 Sensor 5 Equivalence Ratio" of .99 and an "O2 Sensor 5 wide-range Voltage" or 3.3V. I believe this is just the california emissions 5th oxygen sensor though, doesn't effect anything here.

Finally there was a value in my app labeled "O2 Sensor 1 Equivalence Ratio" which read .99 and "O2 Sensor 1 wide-range Voltage" which read 3.3V.

During normal operation and driving, the short term fuel trim would be quite level and my B1S2 sensor would have values bouncing all over the place. When parked, the B1S2 sensor would either read really really low (~0.005V) or really high (~0.889V). The fuel trim would correlate. So when the B1S2 sensor was really low, the fuel trim would shoot up to +20%, and when the B1S2 sensor was really high, the fuel trim would shoot down to -20%. I noticed the vehicle almost stalled whenever the B1S2 was really high, sometimes higher than 0.889V. The B1S2 sensor would perform unpredictably, with it sometimes being low, sometimes high, sometimes a sine wave, and sometimes it would gradually grow from low to high very incrementally, all while idling.

Given this information, would it be logical to conclude that this vehicle is in need of oxygen sensors?

Oh and I pulled off the connector to Bank 2 Sensor 1 A/F sensor and nothing changed.... Bad Sensor???
 

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short-throw dipstick
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Both upstream sensors should be wideband (A/F) in a 2001. There's one narrowband (HO2S) sensor downstream for cat monitoring.

If you disconnect the upstream sensor(s), it uses the default maps to run. Not as good fuel economy, not as good power, but it'll run.

I just replaced an upstream O2 sensor on an LS460 that wasn't throwing any O2 sensor codes; just a P0171 and it would idle rough and hesitate when you pressed the throttle. Sometimes you won't get an O2 sensor code, but do everything you can to make it throw a code (and of course disconnecting the sensor will throw a code).
 

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Discussion Starter #4
EGR


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Both upstream sensors should be wideband (A/F) in a 2001. There's one narrowband (HO2S) sensor downstream for cat monitoring.

If you disconnect the upstream sensor(s), it uses the default maps to run. Not as good fuel economy, not as good power, but it'll run.

I just replaced an upstream O2 sensor on an LS460 that wasn't throwing any O2 sensor codes; just a P0171 and it would idle rough and hesitate when you pressed the throttle. Sometimes you won't get an O2 sensor code, but do everything you can to make it throw a code (and of course disconnecting the sensor will throw a code).
I forgot to mention the vehicle has two codes - a current fault P0440 and a pending fault P0442

How can I test the EGR? Would the EGR really cause the fuel trim to fluctuate like that?
 

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short-throw dipstick
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I forgot to mention the vehicle has two codes - a current fault P0440 and a pending fault P0442

How can I test the EGR? Would the EGR really cause the fuel trim to fluctuate like that?
EGR shouldn't have a significant effect on a MAF-based system like the MZ engines. But EGR issues can cause the driveability problem's you're having. I have a sticking-open EGR valve on my '99 1MZ, and it idles a bit rough.
 

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2010 Camry SE V6
2008 Camry LE
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I forgot to mention the vehicle has two codes - a current fault P0440 and a pending fault P0442



How can I test the EGR? Would the EGR really cause the fuel trim to fluctuate like that?


The whole purpose of EGR is to replace oxygen with an inert gas, to lower combustion temps. So yes, if the EGR is say getting stuck open, it’ll cause the pcm to read rich due to less oxygen in the exhaust, and try to correct by leaning out, when there really isn’t a rich condition.


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Discussion Starter #7
The whole purpose of EGR is to replace oxygen with an inert gas, to lower combustion temps. So yes, if the EGR is say getting stuck open, it’ll cause the pcm to read rich due to less oxygen in the exhaust, and try to correct by leaning out, when there really isn’t a rich condition.


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Okay that makes sense. Is there any other issue that could cause this? I mean if I clean the EGR, throttle body, and IAC and replace the oxygen sensors, this should pretty much be a deal of the past, right?
 

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1994 Camry V6 XLE-J
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cleaning the EGR valve, throttle body(seafoam and toothbrush), and IAC (with it removed from the tb using a jis screwdriver), along with looking for vacuum leaks, loose fitting vacuum hoses, and verifying the egr vsv opens and closes with voltage applied and that it holds a vacuum when the voltage is removed are all things to be done as part of a good maintenance routine, along with plugs (ngk), wires, rotor, distributor, coil packs(denso), and pcv (oem only) replacements as applicable. lastly, please read your haynes thoroughly and familiarize yourself with it as well as the use and contents of the owner's manual (download a copy from the internet for free as it's chock full of specs for your exact car), a dmm and steth as these are the very basics for any diy'er. verify the hot and cold values of the cts and ensure it's within those haynes listed specs or replace it. also, clean the egr downtube and pull the hose off the fuel pressure regulator and check for fuel smell or liquid and replace if found, if so equipped.
if the problem still persists after all this, then replace the 20+ year old ecm as electronics don't last forever.
oh, and get the haynes on obd2 and read it too as it's got lots of good info on how different types of sensors in different locations should behave as it seems yours are acting normally if i'm following your description correctly. when you get more familiar with your obd2 tool, you'll learn how to graph the sensors so you can watch them over time which is more meaningful, especially for the zirconium o2 downstream sensors.
tony
 
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