Hello Jag-gurus,
I just bought an S-type and giving it a service at my local mechanic friend.
It has an idle issue of 'hunting' or surging up and down from about 5-600rpm to about 13-1500rpm when the engine first starts up and then after about 8-10 minutes of idling the surging stops and it sits on about 7-800rpm.
My mechanic has said he has tested the upper vacuum hoses for leaks and there doesn't seem to be any.
I told him about the lower elbow hose below the manifold that I have read about in forums and he wants to know is there a way to know it has failed before taking off the manifold to check?
Does anyone know what these symptoms might suggest as the problem with my car?

Thanks in advance for any advice,
Ben

 

Hi Ben, welcome to the forum.

Is the car driveable before waiting those 8-10 minutes? That's a long time to idle, especially with a cold engine. My '02 V6 is a bit erratic and hesitant for the first minute or so after a cold start, but then again I'm also cranky myself first thing in the morning. But I'm also able to slowly drive away through my neighborhood and within a couple of blocks, the engine quickly behaves itself. No idea what causes this, and no real desire to fix something that is barely broken. The engine only acts up when the car has sat for a long period, such as overnight. Warm starts are always good, even after 8 or 10 hours.

For the elbow under the intake manifold, I don't know what specific symptoms you'd get, perhaps codes P0171 and/or P0174 for a lean condition. I think a lot of people have had that elbow fail and not have any major driveability issues, but don't quote me on that. If you want to investigate further before tearing apart the intake, this link has a good primer on how to troubleshoot vacuum leaks using a scanner:

JagRepair.com - Jaguar Repair Information Resource

 

Thanks for the excellent reply! Much appreciated.
Yes the car is driveable during the surging stage and the idle itself is quite smooth during the surging.
The dash indicator says it’s in fail safe mode and it seems to be starved of power.
Thanks for the link to Jagrepair page and seems very helpful and will pass in to mechanic friend.
I’ve seen references to the MAF sensor or O-rings possibly related to this problem. Could that be the culprit?

cheers,

 

Oh, I should have asked earlier about other symptoms. You should have some corresponding fault codes with that message.

Please post the 5 digit codes (such as P0301) and not just the definition provided by the scanner or code reader. Some generic code definitions are not accurate for Jaguar.

 

You need to get a proper scan run with a code reader that is programmed with Jaguar specific software. Either that, or (as indicated above) bring back the raw codes and share them for interpretation here. Some folks believe that Jaguar and Ford power train DTCs are the same; they are not... For example, Jaguar P1111 means the system flags are set and and ready for emissions testing. Ford P1111 means Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage.

 

Thanks Karl,
I'll get the scanned codes from the mechanic and post those asap!

Cheers,
Ben

 

Hi gents -

Regarding my idle issue - attention is now more on the throttle body - because apparently I don’t have any vacuum leaks according to a smoke test.
I have a DTC code P1584 - Throttle control unit input circuit malfunction.
Also I have a hunch that there could be fuel supply issues with also a code P1233 - Fuel system disabled or offline. Fuel pump sends fuel and car starts up straight away, but there is a very rich smell from the exhaust whilst idling. There is also a fault code B1201 -Fuel sender unit failure.

I took some screenshots of some diagnostics showing STFT and LTFT with some significant variation between bank 1 and bank 2.
Also had oscillating fuel pressure signal and varying throttle position readings.

Anyone able to interpret these symptoms into a diagnosis?

See pics here-


Short term fuel trim


Long term fuel trim


Fuel pressure


Throttle position

Also took a video of the idle if that can help anyone with the diagnosis. I thinks it’s attached?

Thanks for any input or advice.

cheers,
Ben

 

I fixed your comment above. You left out a couple of important words. Gotta be careful with your line of thinking there. A smoke test, while incredibly helpful, still has some limitations like nearly all tests.

Specifically, not all lines are connected to manifold vacuum at idle or when the engine is off. There are various valves that shut off certain lines under different conditions. Consider the vacuum lines that actuate the EGR valve or EVAP system, for example. Unless the engine is running above idle, these valves are commanded closed. The valves are spring-loaded closed, so these muscle lines are isolated during the smoke test. Either line could have a gaping hole in it, but with the line isolated, no smoke will escape. For a successful smoke test, you have to have a very good understanding of what each line does and when it is under vacuum. Sometimes you have to bypass various valves for a truly comprehensive check out.




Ooh, another gotcha to trip you up. Ignore any generic code definition your scanner may give you. You need to use this chart of Jaguar-specific definitions, which are often different than the generic version:

http://www.jagrepair.com/images/Auto...tos/P20001.PDF


For P1584, Jaguar says that is a "throttle body failure", not the "input circuit malfunction" your scanner is telling you. Take a deep breath before entering FullPanicMode™. This is not as bad as it sounds. I had the same fault code about 6 years ago:

https://www.jaguarforums.com/forum/s...m-leak-142564/

I picked up a used throttle body on eBay. I think it was about $75 and was guaranteed to work. Piece of cake to change, and the fault never returned.


Another option is to have your unit rebuilt:

https://www.jaguarforums.com/forum/s...solved-196723/

 

Thanks for the analysis kr.
I’ll grab a used one off eBay.
I have read your post from 2015 and checked out the other links and I figure it must be the throttle body failure.

There are loads to choose from. Do you know if there were differences in the UK cars vs US cars? I’m in Australia. They all have slightly different numbers on the sticker on the bottom of the unit - ending in either A or B? Does that mean anything that you’re aware of?

thanks,
ben

 

You need to fix that before bothering with fuel trims.

 

For the throttle body, I'm not aware of what differences there might be with UK vs. US cars. Just to be safe, it's probably a good idea to get one from your home market, but who knows.

No idea on the part numbers, either. When I bought mine, I didn't think to try getting the same number, but it would be a good idea if possible to do so. Whether the numbers matter, I couldn't tell you, but I lucked out and all was okay. Still is, six years later. But I've got a US market car and the donor was also US.