Interesting fact: I had the cable adjusted nicely when I put the car away for winter in early December. When I pulled the car out of storage the other day, the cable acted like it was overtightened (high idle, car would almost drive itself) so I had to adjust it back. It's very odd to me that sitting for a little under 4 months that the cable would get tighter rather than stretch. For now I have the square turned back one quarter turn. Maybe after driving the cable will need to be readjusted. It was very strange to me.

 

Could have been that Minn. winter. Cold does seem to shrink things, or so they say.

 

YouTube - Seinfeld - The Shrinkage

 

This happens to my car on first start up after I disconnect the battery. High idle, very responsive throttle. Feels like a beast chomping at the bits eager to let rip. It will actually drive up hill at about 40 mph with my foot completely off the gas pedal. All this goes away at the second start up. Sure is awesome though.

 

This could be it. This was the first time I've had to pull the battery for an extended storage. Last year was a milder winter and I had a closer garage to park it, so I could just throw on a trickle charge and drive the car once a month through the winter. This year I had to park in a different storage unit without power and one that doesn't get plowed very often, so I pulled the battery.

 

There is apparently, on some models, a throttle calibration procedure after battery disconnects.

With the key in the running position, with the engine off, floor the accelerator pedal slowly and hold briefly, repeat a total of 5 times, turn key off.

At a guess, this lets the computer read the full range of physical motion available on the particular car. The reason for the 5 times is to avoid unwanted, accidental "calibrations" where the pedal is only pushed part way while the key is in the run position.

 

^ that sounds very plausible, and makes sense to me. Reteaches the throttle position sensor range when its lost? Someone has to try it out though.

 

The was a similar adjustment that was required on my last vehicle to reset the idle air control valve. You started the car with the throttle slightly depressed and then ran for about 15 seconds before shutting off.

Doug

 

Don't forget most OBDII readers will report throttle %...any easy way to see what is really going on.

 

2011-11-16_13-07-29_684.3gp - YouTube

 

Well I never thought there could be any more to say on the subject but I was still bugged about not being able to completely understand what was going on when following the JTIS procedure for adjusting the cable. I was taking another look at mine today to check for slack and played around with removing the clip, moving the notched thing around, etc. Then it suddenly occurred to me (as a structural engineer) that the cable adjusting system is most like the strand anchoring system that is used for post-tension construction.

I am attaching the best illustration I can find as to how a post-tension cable is stressed and anchored. The lowest illustration shows a cable that has been stressed already. There is tension on the strand and what is identified as the wedge keeps the cable from slipping to the right in the illustration. The upper illustration shows how to re-tension the strand (assuming it somehow slackens over time). You pull at the exposed end of the cable which unseats the wedge and frees up the strand so that you can add more tension. When you release the exposed end the cable with wedge slides back into the wedge plate thus locking the strand with the increased tension.

I think the mechanism shown in Sam's video works analogous to this. The thingie with the ridges somehow grabs the cable inside so that you can tension it and the metal clip acts as the wedge once you are all finished.

It would be great if someone could do a dissection of the system to verify what is going on.


Doug

 

I saw a cool documentary on bridge construction where they were using that type of system to tighten the cables on a cable-stay bridge. It was groovy.

Unfortunately, that's not what's happening here. The end of the cable has an attachment brazed or crimped onto it, kinda like bicycle brake cables. The bump on the end of the cable slides into a hole on the plastic cam.

 

But I think the workings of whatever locking mechanism is used for the throttle cable is something similar to the post-tensioned strand. All would be solved it someone had these parts from a car that was being parted and would be willing to dissect.

Doug

 

I have a 1998 XK8 and after reading this post, I went right down to the garage and opened the hood and there it was. The cable with the little adjuster square on it but someone had removed the zip tie. I made an adjustment, replaced the zip tie and I now have WOT!!!!! the responce to just tapping the gas pedal is so much better than before. I will test in the morning but I have a feeling that I am going to be VERY PLEASED!!!

This was a great post thank you one & all!!!!!!!!!!!

 

@Doug,
You adjust the outer sleeve, so by extending it (by taking of the pin), you basically put tension on the cable (i.e. shorten the travel length). What is different to 4.0 cars, is that you can extended it so that the cable becomes too tight (so to short), and due the pin/locking mechanism being made in such a way that it allows to slip a nodge when you over tension the cable making it adjust itself. This way you can never over tighten the cable, and always get a perfect fit.

 

I had to have the throttle body replaced about a month ago at a Jag dealer due to some bad plugs, so I'm assuming the tension on the cable is correct. I can lift it up this much before it becomes tight:



Here is the old throttle body. I'm not sure what some of the indexes or tabs on the cam indicate. Perhaps someone could enlighten those of us (ok, me!) that don't know. I'd be happy to provide pics of other areas of the t/b also, since we have this example to study:







Here's a full shot:

 

Hi Skid Mark nice clear post I have just looked at mine it has about half of slack of yours I think I am going to leave mine its fast enough for me!!
Alan.

 

Hi Alan! Mine's a fast one, too. Jerks back my head off the line if I'm not careful, so no tightening for me either. With half the slack I've got, yours must really go!

 

Hi again Skid Mark thought I would just double check my cable defineatly tighter if I just push it or lift you can see the throttle body move ticks over well and drives smoothely yours might benifit with a tweak!
Good luck Alan.

 

I keep learning more about this adjustment every time I look at it along with the JTIS instructions. I had thought that the purpose of the special adjusting tool (310-101) was to build slack into the cable but when I looked again at the JTIS procedure (which I attached in a previous post) I noticed that the figure above Step 7 (where you step on the pedal with the tool in place) it looks like the tool actually keeps the cam from opening fully against the stop. If you look at Sam's video his adjustment results in the cam hitting the stop--apparently this is not intended by Jaguar.


Doug