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Discussion Starter · #21 ·
Just an update, replaced the intake manifold gasket, no change.

Sprayed brake cleaner all over the place while it was idling and nothing changed the RPM.

The coils I have are all OEM and of course because the 7th gen is coil on plug, I don't have any ignition leads.
 

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Engine may be misfiring at high RPMs and not logged by the ECU and you don't notice it.

The 4 cables between the ignition module to the ignition coils may be shorted and arcing at high RPMs. Check them out and separate them from each other and from the engine.
 

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Discussion Starter · #24 · (Edited)
I reset my codes today after doing an engine flush, followed by a clean oil rinse and another flush. Didn't solve the hesitation but half way through the second flush, had some good carbon come out of the exhaust! I also pulled all the 10 coils I had aside, separated the OEM Denso's and checked for the ones that had the closest resistances across all the terminals and installed them in back in the car.

When the code pops up again, I'll see if I can get the trim in the freeze frame.

To be clear, the the car does not hesitate on gentle throttle or at full throttle regardless of RPM. In other words, if I shift early so my revs are still quite low and put my foot flat, she pulls smoothly, she only start hesitating when I back off the throttle a little.
 

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Discussion Starter · #25 ·
Pulled my live data on the drive to my first appointment today. I believe the system I am using uses
Rectangle Slope Font Plot Line

the terms "short and long-term fuel replenishment storage" instead of "fuel trim". The interesting thing to me is that short and long term, bank one and long term bank 2 make sense but short term bank 2 is drastically higher (I think. It's far enough off to be distorting the graph).
What would that imply?
 

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Lol... Far as I know, we don't have a bank 2 for fuel trims.

Short term fuel trims should usually show in low numbers, as they are just corrections from/to the long term trim. Long term trims should usually be less than 10. Anything > 20 should trip a CEL. Long terms in the 10-20 range may indicate a potential issue that is being corrected by the ECU.
 

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Discussion Starter · #27 ·
Lol... Far as I know, we don't have a bank 2 for fuel trims.
I was thinking the same thing, clearly in reality we only have 1 bank, one exhaust header with 1 set of sensors but something is creating readings for "Bank 3"!

Short term fuel trims should usually show in low numbers, as they are just corrections from/to the long term trim. Long term trims should usually be less than 10. Anything > 20 should trip a CEL. Long terms in the 10-20 range may indicate a potential issue that is being corrected by the ECU.
In doing a little research yesterday evening, my best guess is that the pre-cat sensor may be bad so I ordered one of those. (Which was it's own learning experience! Denso lists the sensors for the specific car vehicle on their website but if you are willing to swap plugs, you can save a fortune on the sensor! Got a new Genuine Denso for $19, Advance Autoparts wanted $125!)
 

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I usually recommend the direct-fits. If you're going to splice in another sensor, I recommend making the splice in the cab where it will be dry.
 

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Discussion Starter · #29 ·
I usually recommend the direct-fits. If you're going to splice in another sensor, I recommend making the splice in the cab where it will be dry.
I'm splicing in the exactly correct sensor (According to Denso), and yes, I will of course try to keep the wiring splice inside the car out of the elements.
A conveniently fitted plastic plug is just not worth $100 to me.
 

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The 3 wires from the Denso O2 sensors are about 5 inches long, so the splices have to be under the car.

You can solder the wires, but I used the splices and taped up with electrical tape. Have not had problems with those splices in years.
 

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Discussion Starter · #32 ·
Well, I replaced the preheat O2 sensor with a brand new denso and the problem persists. Back to thinking I'm going to have to get a smoke test done to look for for vacuum leaks.
 

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What did you use to clean the MAFs? MAF cleaner or something else?

Is the butterfly operating correctly in the OEM airbox? Air filter condition?

What brand fuel are using?
 

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Discussion Starter · #34 ·
What did you use to clean the MAFs? MAF cleaner or something else?

Is the butterfly operating correctly in the OEM airbox? Air filter condition?

What brand fuel are using?
Cleaned the MAFs with electrical contact cleaner, have used it for 20 years. I now have 5x MAFs, switching between them makes no difference so I don't think it's the MAF sensor.

I have noticed several threads talking about the butterfly in the OEM airbox, even seen some pics but mine doesn't seem to have a butterfly or even a place where one looks to be missing.

Brand new air filter.

I will say this, I did another 50 miles in the car today and I'm pretty sure I can tell the difference that performing the 2 sequential engine treatments made. It's definitely seems to run smoother.
 

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Discussion Starter · #35 ·
Cleaned the MAFs with electrical contact cleaner, have used it for 20 years. I now have 5x MAFs, switching between them makes no difference so I don't think it's the MAF sensor.

I have noticed several threads talking about the butterfly in the OEM airbox, even seen some pics but mine doesn't seem to have a butterfly or even a place where one looks to be missing.

Brand new air filter.

I will say this, I did another 50 miles in the car today and I'm pretty sure I can tell the difference that performing the 2 sequential engine treatments made. It's definitely seems to run smoother.
What brand fuel are using?
I live in a big city in Texas, there are only mainstream gas stations around. The first tank I put in, I used premium but since then I've been using standard (87) from mostly Shell.
 

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I have noticed several threads talking about the butterfly in the OEM airbox, even seen some pics but mine doesn't seem to have a butterfly or even a place where one looks to be missing.
Take a pic please.
 

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Discussion Starter · #37 ·
The 3 wires from the Denso O2 sensors are about 5 inches long, so the splices have to be under the car.

You can solder the wires, but I used the splices and taped up with electrical tape. Have not had problems with those splices in years.
Just as a follow up to this comment, the wire that came with the Denso O2 sensor was plenty long enough to pass through the rubber seal so I could do the join inside the cabin. It also came with 4 crimp connectors and heat shrink tubing to do the job well. Having done this now, I would always do it this way in future if it saves me as much.
 

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Discussion Starter · #40 ·
The MAF may be clean and tested good, but it could still malfunction at certain speeds.

I had this problem before with my GTS. The MAF was cleaned and electrically tested good a few times but still showing the P171 code. I swapped in the same MAF from a Lexus, the car ran smooth again, code was clear. So it was the bad MAF.

Replaced with a DENSO MAF and the car has been good ever since.
I have 5 x Denso MAFs, car behaves the same with all of them.
 
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