HI
I have Jaguar S-Type 2008 v6
I have issue that when I am driving the speed increasing and decreasing
It look like if I am press the accelerator and take it off, and the RPM goes up and down (ideal problem) without any action from me
If I am stopping that issue not happening
Note : I change all coils, plugs, and filters

Thanks

Khaled

I have something similar, and people have told me to look for air entering the intake after the MAF sensor. Mine only occurs after the car has been running for a while,

Hello Khaled,

Are you getting any OBD fault codes, such as P0171 or P0174?

2003+ V6 models are prone to damage on the bottom of the resonator on the intake duct. This allows unmetered air to enter downstream of the MAF sensor. This typically causes a lean condition on both banks, but it is very quick to inspect once you know where to look. See post #32 here:

https://www.jaguarforums.com/forum/s...2/#post1934812

Well, I think this is going to be my standard answer for all problems from not on - by the looks of it...

Check the throttle motor CONNECTOR:

https://www.jaguarforums.com/forum/s...nector-288221/

If that connector is not the reason for you problem, you have not lost much by checking it out (not even much time lost). But I think it's worth checking, because if you have for some reason only an intermittent contact there (due to oxidised connector surfaces or a loose connector or due to the wiring to that connector being faulty/intermittent), then I would imagine that you get that revving effect (=RPM up and down)...

torque converter is busted

Rich Here. My 2003 S Type R had the same issue (or something very similar). My problem was at start up, the RPM would race up, eventually after a month of this, the RPM got so high during "idle" that it was dangerous to take it our of Park.

Turned out to be the Throttle body. My local mechanic fixed that and now it has been 6 years with this problem solved.
I see that this throttle body issue has been well documented on other threads in this forum.
Anyways, greatly suggest checking that out.
Cheers,
Rich

Thanks you all for the replies
Now the issue is more worst
When I'm driving, the car is fine.
But as soon as I press on the brake and the car stops, the RPM start goes up and down, then the car shut off.
Especially with the air conditioning on.
Without the air conditioning, the problem gets less, but still there is problem
Furthermore, when I start the car, the voltage is 14.8v.
After a while it goes down to 13.2v.
And when I turn on the air conditioning, it drops to 12.8v..
Also, I noticed that the positive terminal of the battery is a little hot.
Any suggestions ??
Thanks

Ooh, excellent find. Something in that short cable run is acting like a resistor and heating up.

First, check the cleanliness of the mechanical connection between the cable terminal and the battery post. Both surfaces should be clean and bright. You can get a special round brush to clean inside the terminal.

Reinstall the terminal and test again. If little or no improvement, and the cable still gets warm, most likely the crimp connection has failed. The fix is to replace the short cable between the battery and rear power distribution panel.

While you're at it, check the connection where the ground cable attaches to the body. The bolt passes through into the wheelwell. Moisture can wick up via the threads and cause corrosion. So make sure the mating surfaces here are clean and bright, too.

Please be sure to keep us posted. Fingers crossed you've found the root cause.

Actually, I just had another idea about your problem - the problem that you do not seem to have issues when driving, but only when you stop - as you wrote...:

>> When I'm driving, the car is fine. But as soon as I press on the brake and the car stops, the RPM start goes up and down, then the car shut off.

How things work:
When you are driving, you are opening the butterfly-valve inside of the throttle body.
When you stop, the butterfly valve is pretty much closed, and the engine would normally stop, if they had not designed something to stop the engine from stalling in idle...:
Jaguar added a tiny bypass for a bit of air to still go thru the throttle body although the butterfly valve is closed. This tiny bypass prevents the engine from stalling.
And this tiny bypass is called: The idle air control valve on the throttle body.
And if this valve is either broken or the connector to it is not connected, or the contacts of that connector are corroded or the cable to that connector are damaged (mice?), then you would experience that problem, which you are having, I suppose...

Is this valve a separate unit replaceable on its own, or is it built into the throttle body? I'm not seeing a separate IAC on the wiring diagrams, like other vehicles have.

Another possibility is with the PCV system. I found some interesting details on the PCV system a few years ago. It's not like most vehicles, which are closed or nearly so at idle. The Jaguar system is opposite, and it fully open at idle and deliberately bypasses a known amount of metered air around the throttle body when the butterfly valve is closed. More details in post #21 here, also post #25:

https://www.jaguarforums.com/forum/s...2/#post2591435

Those specifics are for the early V6, but I believe it is also applicable on later models. If my theory is correct, it might be worth gambling on a new PCV valve. It's easy to change on a later model, unlike the early V6. Check the associated lines for damage, too.

Sounds like a TC (torque conv) problem.

2003 S Type R

I had a similar problem a few years back; the idle TPM increased over a period of several weeks to the point I was afraid to put it into Drive.
When I did I had to slam on the brakes, which put grooves in the disk.
The problem was the throttle body. which when replaced or fixed solved the problem.
Cheers,
Rich

> Is this valve a separate unit replaceable on its own, or is it built into the throttle body? I'm not seeing a separate IAC on the wiring diagrams, like other vehicles have.

OK, Karl, looks like you are right there and I was too excited too fast thinking this must be it.
Yes, I knew that other cars have an idle air bypass, and I even found an indication, that the S-Type has it, but it looks like only the 2000-2002 V8 S-Type have it.
The two connectors going to the throttle body of the 2008 S-Type would then be the actuator motor of the butterfly and the valve position sensor (Denso 198500-3300).

Nevertheless, the failure mode would fit with my (wrong) diagnosis... Thus: How is the idle air issue solved on the V6 2008 S-Type? Whatever that solution is, this could still be, where the problem lies. Is it possible that there is somewhere a small butterfly-valve-bypass-channel inside of the throttle body, which is simply blocked?