So, like many others here, I have been beset by the "high idle syndrome". Twice, while at a main dealer on a seperate matter, the TPS was reset/tuned or whatever they do to it! It seemed to cure it, but it returned again and the second reset was done for free. Anyway, I did all the usual things, TB clean, return spring replaced with a beefed up version. Idle speed control valve replaced, AFM replaced etc. etc. Fortunately, I have a donor car, so the process of elimination wasn't too painful. Still no joy, with it coming and going until it became more constant, idling between 1800 and 2000 rpm. I wished for the old days when the idle was adjusted by a simple turn on the throttle stop screw..................so I thought, what is there to lose?

The screw in question is on the side of the throttle body, facing towards the front of the car. It is a small grub screw, adjusted with an allen key and is accessible without having to take anything apart. Its a tight spot, so an allen key with a short end is advisable, or maybe just shorten one? Dont know the exact size, but its small!

Anyway, I turned the screw back a bit, ran the engine and noticed a slight drop, back another bit and the idle was noticeably lower on the rev counter, another tweak and I got it settled on 700 rpm! I then had to take a 60 mile trip and arrived with it still idling at 700! We shall see how it goes, but I suspect that over time components including the ecu try constantly to manage a system that has gone out of sync somewhat, so that replacing parts just gives it new work to do. Whatever the reasons, this simple approach seems to have worked. Watch this space! Incidentally, there was no effect on the general running when driving, everything did what it was supposed to do.

May be worth a try if all else fails, or even before you start getting into the complicated and costly stuff.

 

The reason most screws are turned IN is because the throttle plate sticks and opening it a little keeps the plate from touching the bore. It is easier than cleaning the throttle.

bob gauff

 

Thanks for the tips, I am also finding a good old simpler way to adjust the idling speed without going through the TB and ECU.
My 95 XJ6 is experiencing the same problem today with 1500 rpm at "N" and 900 rpm at "D",
Did your problem come back? I will probably do the adjustment this weekend.

 

I am happy to report that she is still running sweet as a nut. No re-occurence so far, touch wood. (Burr Walnut!!)

 

Hi,
Over the weekend,
I was not able to find the said " small grub screw adjustable with an allen key" on the TB, so, I tried a few things, the RPM still idles around 1500 on P or N gears.

Would you advise me more detail if with a photo on where the "grub screw" is?

Thanks in advance.

Mine is a 95 X300 3.2L, this shouldn't make the TB much different, I hope.

 

I dont think there is any difference between our models (96 x300 4.0l) but I'm away at the moment so a picture isn't possible. But anyway, mine is a right hand drive to start with. If you look down onto the throttle and rotate the throttle arm by hand (normally operated with the throttle cable) you will notice the black section with the spring wound around it, turning.This "black section" is housed in the cavity or space directly below the top of the throttle body. It has a little upstand or tab which comes to rest against the end of the grub screw, thus, adjusting the screw, in or out sets the tab/throttle, and so increases or decreases the idle. On my car, the part of the screw that needs to be accessed is between the throttle body and the front of the car. If you look down and see the aforementioned tab etc, you will see the screw. Hope it helps and sorry for the delay, but I was having grief with the computer!!

Hope this helps.

 

Thanks a lot for the detail description.
I will definitely try it out this weekend.
cheers.

 

Your advise paid off again today. Cleaned the Throttle Body twice today, and did not want to tough "that allen screw" as I assumed it was factory set. One turn and the idle fell to where it should be. Thanks you.

 

Idled fine until a local shop cleaned the throttle body. Then the high idle problem started. Replaced throttle position sensor under the throttle body. Adjusted the throttle setting screw. No improvement. Ugh. Time for a trip to the Jag dealer?

 

Yup.

You'll need a TPS Reset. You might be able to do that on your own, if you're willing to manually adjust the TPS on the throttle. It's a little bit of working in the dark. (If you search the forums, you'll find posts on how it's done manually)

OR

You can find a shop that has a diagnostic computer with specialized Jaguar software.

The Jag Dealer should only charge you for 1 hour of labor, even though it'll take them 20 minutes tops.

 

I got the same problem on my xj6 1972...Pass 1200rpm to 300 ( on D )

 

See the previous post about getting your TPS reset.

I have seen some throttle bodies with an idle air adjustment screw, but neither of my two AJ16 engines had them. I would ignore that recommendation. If you hunt long enough, you'll find a post with a picture of their throttle body showing a screw where you probably don't have one.

If you're throttle body is clean, and you have to take it off the car to clean it, which is easy, AND you can confirm you have no vacuum leaks, a TPS reset will cure your issue. You can also check some other sensors, such as the coolant temp sensor, and the MAF, but the TPS will have to be reset, or manually adjusted, which takes a little work.

If you have a lumpy idle, where the rpms will constantly hunt, then that's a different problem. (probably oxygen sensors)

 

I have a lumpy idle after the cars been running for a few minutes. It’s fine before and also fine when fully heated up ?

I replaced one o2 sensor to cure rich running and bad emissions a couple of weeks ago and the fuel mpg has increased dramatically and the emissions. Are now fine !

bit would that lumpy idle be the old o2 sensor not keeping up with the new one possibly 🤔

 

You really should replace all the oxygen sensors at the same time. It's like changing out only one headlight. You know the other one is not long for this world. Replace it and see what happens.

 

Other one is on the way and I’ll change it at the weekend 👌🏻