All advice and experiences are greatly appreciated.

Hello. I have a 03’ STR. 115k miles. I’ve had a come and go P0174 code for literally almost a year now, ever since I purchased the car. My trims are not bad but the code returns.
The car runs strong. This code appears after a few sessions of “kickdown” I guess people call it. For me it’s full throttle, flooring the car every now and then, showing off. Then the “Restricted Performance”(RP) code follows and within 3-5 minutes of driving the RP code goes away and no more limp mode. The Check engine light clears itself the next day.. and this has been the case NUMEROUS times. I only have the high trim at Idle, when driving the trims are perfect which is probably why the RP code goes away so fast.
The car starts perfectly fine.. my mechanic has said before he’s not even sure why there’s a code because the engine is strong and runs perfectly fine.
I guess my only option is get a smoke test? Thats if I replace the O2 and my Trims still run high.
Can it be the O ring? Or would that effect both banks.

STFT B1 1-4%
LTFT B1 1-4%
STFT B2 5-7%
LTFT B2 sits at 14% currently

I’ve replaced sparks and coils
I just recently bought a new DENSO MAF sensor
I’ve purchased 4 USED O2 Sensors. (I’m aware this Could be the issue). I have a brand new DENSO upstream sensor that I will try to get replaced tomorrow.
I’m running stock air box with a mina gallery Chrome Elbow
I’m told if it were my catalytic converter, my trims would be high even when driving.
I do have a slightly modified Brake booster hose due to not being able to find a OEM STR one, I ended up used one from another Jaguar with the same connectors. Everything plugged in fine.
Before you waste your time, I’m aware and I know there’s many forums on this code.. I’ve looked at them all. Mine doesn’t seem to follow suit with theirs.

Let me know if I can give any more information that can help.

 

With one bank way out it cannot be anything common to both banks - so can't be MAF.

Sounds like an air leak affecting that one bank.

 

How do you feel about the used O2 sensors?

 

Everything points to an air leak. Nothing to the O2 sensor.

 

So Smoke test is my best option? Is there any other test I should search for.

 

The first thing I will say is that you need genuine Denso heated O2 sensors.
Patern part ones can give problems.
So can fake Denso ones!!
The original Denso sensors should have the Dense logo on the actual metal part of thed sensor. The grey plastic connector should be the same shade of grey as the original.
The fake ones do not have 'Denso' on the sensor and the grey plastic is lighter than the original.

The effort in removing the sensors can make them fail, so second hand ones may also be a bad idea.

I try and get 'new old stock' jaguar boxed sensors.

 

How do you get New old stock sensors.
i got a new one off of Rockauto.com, I see FCP Euro sells them also. The used one and the brand new one are reading the same.. the pair of used Densos I bought work just fine. With swapping and purchasing new ones the trims remain consistent, pointing towards some sort of leak.

 

There is another thread covering this same issue with the same vehicle.

Have a competent shop perform a smoke test to determine the source of the P0174 and correct it.

 

I’ve looked at them all. I’ll take another look. Thanks