So here is an order of events as I’m trying to figure out why I’m having hesitation problems in my idling.

Replaced all 4 oxygen sensors
them fuel pump went bad , so replaced fuel pump and fuel filter. When I road tested it, ran great. No hesitation, fast off the line.
Next day, I got in car and started driving it and started getting a hesitation at idle like a vacuum leak. Then I would get restricted performance popping up occasionally. I ran the codes and it said possible EVAP problem so I retraced all my vacuum lines and electrical from the gas tank. Electrical good and I also did a smoke test and no vacuum leaks. I had also replaced the coolant sensor and the MAF sensor.
my code PO453 went away but PO174 and PO171 popped up. I did a fuel pressure test off the stradler valve and it’s 35 psi at idle. When I blocked the vacuum line that goes to the pressure regulator, it jumped up to 41. When I shut off the engine, the pressure would go from 35 to 40.
I'm thinking it’s the fuel pressure regulator but open to ideas.
This is very frustrating because I haven’t had any problem since I’ve owned it since 2019.
Also I changed my fuel filter before the fuel pump went bad. I was thinking longshot that maybe some sediment got into the fuel filter after I changed the fuel pump.

 

Fully warmed up engine, do the usual fuel trims checks & report their values.

 

What do you mean "Fuel Trim Checks"?

 

Do you have a scanner that displays live data?

 

My fuel pressure regulator went out couple years ago, the little diaphram stuck. No hesitation that I recall, but codes for too rich very intermittently. Finally figured out that it was the fuel pressure regulator. It defaults to 41psi without vacuum. Sounds like you can rule out the pressure regulator since yours is going lean and probably not the pump or filter either since pressures are within spec. Would not expect injectors since its lean on both banks. What about those new O2 sensors? I don't know about you, but I've sure gotten some low quality replacement parts in recent years, even from Jaguar, that didn't last long or didn't work right out of the box. So much so that's where I check first now when a repair goes awry.

I might also suggest do the smoke test again. Often, when I do that, I just have a hard time seeing it and so I suspect a small leak could be easily missed. Get one of those bazillion lumen flashlights. That helps me. Sounds like you had a lot of stuff apart and its often happened to me that I miss getting a vacuum hose re-attached or a gasket misaligned or a hose clamp I didn't tighten during re-assembly, leading to a vacuum leak. Good luck.

 

yes I do. I’ll check it today.

 

hello, did you you try to change your PCV Valve

 

Not sure how to decipher these

 

STFT 1 = Short Term Fuel Trim.
The ‘1’ is for Bank 1
STFT 2 is like above but, for bank 2.

LTFT 1 & 2 is Long Term Fuel Trim bank 1 & 2.
LTFT is a much slower responding fuel trim adjustment.
STFT is a much faster responding fuel trim reading.
The LTFT is considered ok if it’s in the -10% to +10% range.

Your LTFT’s for both banks are above the threshold. This means overall that your ECM is trying to add more fuel. There are *many* reasons that can cause the P0171/174 B1&2 lean codes. Vacuum leaks in the air intake tube, intake manifold gaskets, dirty MAF (or just about all aftermarket MAF) sensors, vacuum leaks in the part load breather tube, full load breather tube, brake booster vacuum pipe leaking air from the o ring inside the brass insert under the throttle body, low fuel pressure, clogged fuel filter, no o ring on top of the engine oil dipstick. You get the idea. There’s many ways to have a vacuum leak, faulty MAF sensor or low fuel pressure to cause these codes.

 

BTW, there’s technically no PCV on these engines. It’s a small orifice on the B2 valve (cam) cover. It must be free of any oil sludge. A completely clogged shut orifice won’t cause lean codes.

 

Is there way of checking the MAF sensor? I originally replaced my original with aftermarket and then switched back to my original. Is there anyway to test them to see if they are both bad or good?

 

Fortunately you kept the original one. You must clean the resistors down inside the tube. If they look dark or fuzzy, that’s going to contribute to the lean codes. The single ‘bulb’ like thingy is the incoming air temperature sensor. I’ve used brake cleaner and compressed air on hundreds of those MAF’s and never had a problem. If it makes you feel better, get actual MAF sensor cleaner and be liberal with it. To answer your question, the LTFT’s should come down *IF* the aftermarket MAF sensor changed to the original cleaned Denso sensor makes a difference. I know there is a set value for the MAF grams per second reading but, I don’t know the exact number. Just clean the original Denso sensor first then re-evaluate. Maybe go drive it a bit if you can.

 

This is how to test MAF with ODB2
JagRepair.com - Jaguar Repair Information Resource

 

Well I got the codes all situated. They are not showing up anymore but another problem has come up.
When I reach about 50mph there is a weird noise from under the car. It seems to go away when I lift up on gas and I can accelerate past 50 but it still makes a strange noise. It kind of seem like it is starving for gas, so I checked the Fuel pressure.
When I start the car the pressure is at 33psi. When I rev it and hold it at high RPM, it goes to 38 then back to 33. I turn off the ignition and pressure gauge says 30.5 PSI. When I let it set for 2 minutes it goes to 34psi. When I let it set for 3 more minutes it was at 39psi. Any comments or ideas? TIA

 

I wouldn’t be too concerned with the fuel pressure at the moment. Does the engine seem to have good power going down the road?

Tell us a little bit more about this noise underneath. How many miles on this car? I would check engine/transmission mounts, driveshaft jurid couplers at the transmission and differential then check driveshaft center support bearing for excessive movement.

 

Back in December:
Re-placed all 4 oxygen sensors
them fuel pump went bad , so replaced fuel pump and fuel filter. When I road tested it, ran great. No hesitation, fast off the line.
Next day, I got in car and started driving it and started getting a hesitation at idle like a vacuum leak. Then I would get restricted performance popping up occasionally. I ran the codes and it said possible EVAP problem so I retraced all my vacuum lines and electrical from the gas tank. Electrical good and I also did a smoke test and no vacuum leaks. I had also replaced the coolant sensor and the MAF sensor.
My code PO453 went away but PO174 and PO171 popped up. I did a fuel pressure test off the stradler valve and it’s 35 psi at idle. When I blocked the vacuum line that goes to the pressure regulator, it jumped up to 41. When I shut off the engine, the pressure would go from 35 to 40.
I'm thinking it’s the fuel pressure regulator but open to ideas.
I forgot to re-install the air filter, so I did and the PO174 and PO171 codes went away.
This is very frustrating because I haven’t had any problem since I’ve owned it since 2019.
Also I changed my fuel filter before the fuel pump went bad. I have since re-checked the fuel filter and it is good.
This is very frustrating because I haven’t had any problem since I’ve owned it since 2019. Car has 145,000.
When I reach about 50mph there is a weird noise from under the car. It seems to go away when I lift up on gas and I can accelerate past 50 but it still makes a strange noise. It kind of seem like it is starving for gas, so I checked the Fuel pressure.

1/31:
When I start the car the pressure is at 33psi. When I rev it and hold it at high RPM, it goes to 38 then back to 33. I turn off the ignition and pressure gauge says 30.5 PSI. When I let it set for 2 minutes it goes to 34psi. When I let it set for 3 more minutes it was at 39psi. Any comments or ideas? TIA

Today 2/1:
I took out to run a errand. When I get up 50 it seems to hesitate and when I let of gas and the step on the gas it smooth's out. Power wise, when I step on it it moves, very fast like it should. At idle I notice a sight surge, but the rpm gauge barely shows it.
.

 

Feb 1st:
Noticed something else this afternoon, When I take off the vacuum line off the Fuel Pressure Regulator, the idle smooth's out. When I reattach it, the idle starts surging again, very slightly.

 

Probably time to change the vacuum pipes then, they do go brittle & split.