I have a Jag S type 2004 2.5 V6
May I know the following correct data during idle?
1. Air flow rate (g/s), current is about 6.06~6.36
2. Engine RPM, current is about 686~718
3. TPS throttle position, current is about 4.7~5.1%

The car has idle stalling problem
I had replace mostly engine sensors except MAF, and TPS
I had also replace intake manifold, filter, Engine sealing, ignition coils, spark plugs....

The ODB2 and other computer doesn't show any error code.

 

Use OBD but first get engine hot, then park
1. is it idling CL (closed loop)
2. are all the OBD monitors set? If not, which afre unhappy?
3. what are the fuel trims?
4. any pending codes? (must have either P1111 or P1000)

 

Your scanner can't see deep enough into the car?
What scanner are you using and can you get the car hooked up to the dealer tool SDD?
You may have codes that will help with the repair but your device can't see them.
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Here's a good primer on using fuel trims to check for vacuum leaks:

JagRepair.com - Jaguar Repair Information Resource


If I had to wager a bet on the root cause, a potential vacuum leak is the first thing I'd want to rule out.

If you still suspect the MAF sensor, I vaguely remember somebody saying you can temporarily unplug it for troubleshooting. Of course you will now get a fault code for the missing input, but that is a normal response from the computer. With the sensor disconnected, the computer will substitute preprogrammed values. If the engine runs better, the sensor was probably bad. If no change, the problem is elsewhere.

 

1. Yes, it is closed loop (idling)
2. Yes, All OBD monitors are set well
3. The fuel pressure is about 380 kPA
4. There's no pending codes or error code

 

Actually, the repair shop help me scan all codes and there is no errors.
I had send my car to the shop last month to replace all suspensions, brake system, changing fluid(Engine oil...etc), replace all engine sealing, spark plus...etc.
It's very strange because that's no error codes show on their computer. (No missing fire, MAF, TPS, MAP...etc. is fine)

 

You mean STFT (short-term fuel trim) and the LTFT (long-term fuel trim)?
My OBDII does have short-term fuel trim? what kind data or graphic should I provide?
I use an app named Infocar. Below is the OBD I use


Please kindly advise the clear procedure to get the data?
For exp. warm up the car until the water temperature reach 90 degree...etc.

 

Hmm, that is odd if your scanner does not show STFT. Does it show any live data, or is it strictly a code reader?

If able to read live data, watch the STFT. Warm the engine fully. Record the STFT on both banks at idle. Then rev the engine to approximately 2500 RPM and hold it there until the STFT stabilizes. If you have a vacuum leak, the STFT will be high at idle when vacuum is greatest. The computer is commanding increased fuel flow to compensate for unmetered air leaking into the intake manifold. At higher RPM, the vacuum decreases, the unmetered air leakage drops, and so does the STFT.

If STFT stays relatively similar at idle and 2500 RPM, you're not dealing with a vacuum leak.

 

Forgot to add something, although it may be in those links I gave earlier. While watching the STFT, momentarily unseat the dipstick. This induces a vacuum leak (via the crankcase ventilation system). You should see a reaction similar to any other vacuum leak. Creating this intentional vacuum leak will help you see what to expect while chasing any others.

 

Greatly thanks for your prompt reply
My OBD2 has live data function but I don't know how to read it. Maybe I will use your method and upload the data sometime this week
Do you have any similar live data which can show me how the curve will look like? This will help me understand how vacuum leak looks like.

I drive about 20km and get some data as attachment.

 

I record the data and upload to Youtube

 

These cars have 2 banks. 2 O2 sensors each bank. You always have pending code P1111 (good) or P1000 (hope not).

You posted STFTs so tool can show them.

Normal fuel trims test is hot engine parked. At idle 4 readings (banks 1 & 2, STFTs & LTFTs). Again at about 2500rpm, same readings.

No need for graphs etc to tell if there's any air leak.

 

I'm not super well-versed in the use of fuel trims, but here's a good video explaining the process to determine if a vacuum leak is present:


Note how the guy induced a known vacuum leak (by disconnecting a small hose) and used that to show what you'd see on your scanner with an actual leak that is not so obvious.

Also note how he suggest adding long and short term trims for each bank to get a total. I like this idea very much, as long or short term trim values by themselves may be misleading.

I watched your video again and added the long and short term values, as suggested above. At idle, the numbers added up to approximately -2.4. At 2500+ RPM, I'm seeing more like -15. That's quite a difference. If I understand the process correctly, this is pointing to a vacuum leak on bank 1.

You only showed bank 1 data. Take a look at bank 2 and see if those values are comparable.

As previously suggested, don't forget to unseat the dipstick or unplug a vacuum hose to create a known leak. See how the numbers change to give you an idea of what you'd see with an actual leak.

If indeed you have a vacuum leak on bank 1, try spraying some starting fluid at the likely areas for a leak. If the starting fluid is drawn into the manifold through the vacuum leak, the short term trim will drop in response to the extra fuel, and then shoot back up when the fuel is consumed.

 

Here are some fuel trim for your reference
Please kindly advise if any error

 

Beg pardon but truly curious.

How hot? I've read that these temp gauges sit between 180 & 230°F, then if getting hot, very suddenly shoot up and, it is reported, at that point "it is too late." This was not clarified but my F150 (Ford) does this and then head gaskets fail... A known S-Type issue. The oil gauge in the F150 is a 6-15 psi SWITCH. Maybe the thermostats are also.

 

That's not really a known S-Type issue. Hardly any affected.

Normal hot i.e. properly warmed up including cats.

You could look at the many many previous posts on fuel trims to save a LOT of time and just follow them.