Pulsing RPMs after cat/O2 sensor/exhaust replacement…

[Babyfood1217]

Vehicle: 2002 Sport SR5 - EPA emissions (non-CARB)

Recently had my rear cat stolen, and just had a chance to install the replacement parts last night (pretty much all Walker stuff). New O2 sensors (upstream AND downstream) along with the new cat and muffler. New exhaust gaskets at each joint.

Fired it up, and now my RPM pulsates. At idle, during acceleration, and during steady throttle, there’s an a consistent pulse in the RPM, regardless of where the needle is on the tach. Pulse seems to be between 50-100rpm, according to a visual check of the tach, and according to a couple different OBD reader apps on my phone. No codes are being thrown, no CEL, and per the apps, all parameters look to be good. (I have an ELM327 reader, and have used DashCommand, CarScanner, and inCarDoc apps).

Vehicle ran fine before this theft, this has appeared only after new parts install.

Despite getting no codes to suggest there being an issue, I’m tempted to get a new MAF, since a lot of folks refer to it being a culprit when tracking down RPM issues (though I haven’t read of a problem matching mine).

Any thoughts? When new O2 sensors are put in, do you have to replace other bits at the same time? Or reset anything (I’ve swapped O2 sensors before, but don’t recall resetting/changing other stuff). Do new catalytic converters break-in in such a way to that would cause this type of pulsing RPM issue?


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[brillo_76]

What year of 3rd gen emmisions are we dealing with?

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[diverscale]

my guess is that your first o2 sensor needs replacement

 

[Babyfood1217]

What year of 3rd gen emmisions are we dealing with?

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Oops, edited above, but EPA non-CARB.


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[Babyfood1217]

my guess is that your first o2 sensor needs replacement

I put in a brand new Denso for the upstream sensor. I can wrap my head around new parts being crap, but would that explain the specific symptoms I’m experiencing? When o2 sensors have gone bad before, I’ve at least gotten a CEL. (The downstream was an aftermarket, that what the shop had at the time)


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[Bad Luck]

I put in a brand new Denso for the upstream sensor. I can wrap my head around new parts being crap, but would that explain the specific symptoms I’m experiencing? When o2 sensors have gone bad before, I’ve at least gotten a CEL. (The downstream was an aftermarket, that what the shop had at the time)


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Where did you buy the Denso oxygen sensors from? What part numbers did you buy?

 

[brillo_76]

Did you buy your sensor from Toyota, Rock auto or an auto-parts store? As its quite possible if you didn't you got a counterfeit one. Thus why it doesn't work properly.

 

[Babyfood1217]

Where did you buy the Denso oxygen sensors from? What part numbers did you buy?

Did you buy your sensor from Toyota, Rock auto or an auto-parts store? As its quite possible if you didn't you got a counterfeit one. Thus why it doesn't work properly.

Denso #234-9002

Purchased off Amazon last year as I had some credit I wanted to use and thought I would stockpile some regular maintenance stuffs, just never got around to doing it. Sensor has been sitting in its box ever since.


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[Babyfood1217]

Denso #234-9002

Purchased off Amazon last year as I had some credit I wanted to use and thought I would stockpile some regular maintenance stuffs, just never got around to doing it. Sensor has been sitting in its box ever since.


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[Babyfood1217]

I’m kinda going a through a crash course in vehicle issue diagnosing here, so I wonder if what I’m experiencing is the phenomena often referred to as “hunting”?

I just read a reference to trying to isolate the issue by unplugging the o2 sensor, causing it to go into an “open loop” state. A CEL would likely come on, an there would likely be a loss of power, but if the “hunting/surging” also disappeared, that could be a good indicator that it is indeed a faulty O2 sensor. Does that sound right, or am I understanding that concept correctly?


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[Bad Luck]

Denso #234-9002

Purchased off Amazon last year as I had some credit I wanted to use and thought I would stockpile some regular maintenance stuffs, just never got around to doing it. Sensor has been sitting in its box ever since.


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That's the correct part number, but amazon and ebay are full of knockoffs so it could be a bad sensor. Do you still have the old sensor?

 

[Babyfood1217]

That's the correct part number, but amazon and ebay are full of knockoffs so it could be a bad sensor. Do you still have the old sensor?

I do, suspect you’re gonna suggest tossing it on to see what happens


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[brillo_76]

I do, suspect you’re gonna suggest tossing it on to see what happens


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That's what I would do. As you really gotta watch Amazon and ebay sadly.



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[diverscale]

I said that because I had pulsating RPM's when in closed loop (You'll see that you don't have pulsation in WOT) and my problem was my first O2 sensor, without a check engine. And that first o2 sensor is an air fuel ratio sensor. got it from Rock Auto not from amazon, it's too risky.

 

[brillo_76]

I said that because I had pulsating RPM's when in closed loop (You'll see that you don't have pulsation in WOT) and my problem was my first O2 sensor, without a check engine. And that first o2 sensor is an air fuel ratio sensor. got it from Rock Auto not from amazon, it's too risky.

Good to know you seen this pulsing before. I always pull my o2 sensors from Rock Auto. Always had great success.

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[Babyfood1217]

Welp, I tossed the old air/fuel sensor back on. Truck runs just fine now. WTF.

Looking at the NEW Denso I put on, AFAIK, it’s legit Denso, so perhaps it was just a dud?. See pic for the etching…

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[brillo_76]

Welp, I tossed the old air/fuel sensor back on. Truck runs just fine now. WTF.

Looking at the NEW Denso I put on, AFAIK, it’s legit Denso, so perhaps it was just a dud?. See pic for the etching…

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I haven't ever seen one bad from ledgit sources. They are definitely getting better at making them look ledgit.

How was the price comparable to the oem one? From Rock auto or autoparts stores? If they are not in the ball park of those sources. It's quite possible it's fake.

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[Bad Luck]

I agree with Brillo. They make some very convincing counterfeits now.

 

[Babyfood1217]

I haven't ever seen one bad from ledgit sources. They are definitely getting better at making them look ledgit.

How was the price comparable to the oem one? From Rock auto or autoparts stores? If they are not in the ball park of those sources. It's quite possible it's fake.

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I paid around $140-150 for this, i’d have to check to find a specific number. When searching around for replacements, I definitely did see some were priced out around the 35 to 50 mark, not listed as Denso necessarily, or even Bosch, but I wouldn’t suspect a part that cheap to perform at all, let alone as well as an original piece that cost 45 times as much.

I suppose it’s possible that I bought an expensive knock off, or that I got a dud despite it being legit. Could the fact that it had been sitting on my shelf for a number of months before I actually used it have affected anything, just out of curiosity? I can’t quite wrap my head around any reason why that would make a difference, considering all the where in tear a normal part would get, but you never know.


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[brillo_76]

I paid around $140-150 for this, i’d have to check to find a specific number. When searching around for replacements, I definitely did see some were priced out around the 35 to 50 mark, not listed as Denso necessarily, or even Bosch, but I wouldn’t suspect a part that cheap to perform at all, let alone as well as an original piece that cost 45 times as much.

I suppose it’s possible that I bought an expensive knock off, or that I got a dud despite it being legit. Could the fact that it had been sitting on my shelf for a number of months before I actually used it have affected anything, just out of curiosity? I can’t quite wrap my head around any reason why that would make a difference, considering all the where in tear a normal part would get, but you never know.


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Sitting on the shelf for a few years shouldn't hurt it any.

That's around what that front one would cost.

I just can't say I ever seen a denso sensor bad from a reputable sources.

I guess it's possible ones bad and it's possible that it's a knock off too.

Regardless, you know what caused the pulsating rpm is from a bad sensor.

I don't know what to say. I think it was a counterfeit sensor but I could be wrong.

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