Yes guys, thank you all. The adjustment on my '99 XK8 Drop top took 3 notches. Fairly simple on the '99 4.0/ cable adjustment is right next to the throttle body lever. Yes, insure you replace the tie strap.

Definitely responds differently. or I guess till the computer re adjusts itself.

thanks again Rich

 

I did mine yesterday. Two turns. Very nice change in feel. Much more responsive. Does this affect the gas pedal? My pedal used to feel like the top of it was pointed too close to the floor. Your foot had to tip in too much with no throttle. Now it feels like the gas pedal is as it should be. I didn't measure it before the adjustment so I can't be sure if it really changed anything.

 

Thanks to all contributors on this very informative thread. There is however another adjustment for the throttle. I discovered, to my own dismay, while removing the carpet which has confounded me.
I pulled the cap off the floor of what I thought was a simple throttle pedal stop. In reinstalation, I see it is much more complicated. Complicated usually means important. The stop must be adjustable for a reason.
My initial thought was to shove throttle down to first indent without stressing the mechanism then place the floor stop just touching the bottom of the pedal. But now after soaking up the thread I can't help but wonder if there shouldn't be a gapped clearance Beneith the pedal to allow for a kick down.
The stud coming off the floor is a 4 sided afair with threads on two sides. The wire clip that secures the plastic stop seems to be designed to slide on the stud and then twist a quarter turn to lock in place.
I realize that this is the opposite end of the throttle from where this discussion has been engaged, but if someone has knowledge of this pedal stop I would certainly be interests to hear it.

1999 XK8 Cabriolet Base. (Gwendelyn)

 

Here's some info on the Throttle Pedal Stop from the jtis

 

Well I'm not sure if it is a stop or a switch. I'll see if I can depress it by hand (like a switch) or if fixed like a stop.
If it's a stop I suppose once the throttle is fully opened the engine is at max acceleration. At that point I would raise the stop to the bottom of the pedal.
If a switch I will raise it slightly so the switch actuates just pryer to fully opened.
Sure am glad I didn't pull it off and break anything while getting under the carpet.
I appreciate any input and thanks to all who have kept this thread going.


:

Merry Christmas

 

I have never tried removing this piece but it certainly has the feel of a switch versus just a stop. You can tell easier by getting down there and pushing down on the switch with your fingers--there is first a partial stop (or click) and then the switch finally bottoms out.

Doug

 

On my 2001 XK8 is is definately a stop, not a switch. I can pull the little black piece of plastic off and there is just a stud there, nothing more. When I push the accelerator pedal down, it comes to a stop about a half inch before touching the stop and then it requires a rather hard push to move it the rest of the way. Reading the above info, it seems that for some model years there was a two stage system, with both a switch and then, if the switch did not work, the position of the pedal activated the "kickdown" feature. In effect, this seems to be nothing more than than a regular old "passing gear" that American cars with automatic transmissions have had since at least the 60's.

Of course, those of us who had muscle cars were also treated to the opening of the four barrell (or more) and that accompanying noise along with the kickdown to a lower gear was a rush. Depending upon how fast you were going, it might even produce some wheelspin.

On an accompanying note, I very seldom push the pedal to the floor. In fact, in five years, I have probably only done it four or five times. The first time was on my way back to Baton Rouge from Dallas, when I first bought the car. I got some gas and got onto the interstate in a very rural area with very little traffic, so I decided to floor it just to see what it had. It took off OK, but I was a bit disappointed. The car had been detailed before I bought it and it was immaculate, and I only drive it on weekends when the weather is nice, so it was several months and probably almost a year before I even had to vacuum it out. When I did, and took out the floor mat that the previous owner had put in it, it was a very thick floor mat that actually was covering the stop, meaning that when I had floored it, it probably had well over half an inch that it could have gone. So, I moved that out of the way and went for a ride to test it, and I noticed a great deal more acceleration. A year or more later, I saw a post on here about the kickdown and realized that I still had not pushed the pedal all the way to the floor, so I went out and tried it again. This time it finally performed as I had expected.

Unlike many of the people who come on here disappointed because the XK8 is not a FAST car from 0-60, I knew what I was getting, and that is a car with more than adequate performance for any reasonable driver, but not a stoplight warrior to run around racing modern cars that can go 0-60 in well under six seconds. These cars were fairly fast in relation to the other cars out there when they first came out 1997, but not so much 12-15 years later with the advancements that the car companies have been making in engine performance.

 

Agree with KevinD. I might have floored the car perhaps a half dozen times in the 6 years I have owned it. The car is very deceiving in that there is no headslam from the acceleration (like with my old Corvette) but rather a very smooth and competent delivery of power. I remember the first time I saw the car and the owner took me for a test drive. He was going up some local back street and had it floored and while it didn't feel like we were going fast the speedo indicated 70mph in no time.

These cars were produced when the 300 horsepower club was pretty rarefied territory. But these days there are many mainstream Asian sedans pushing 300 hp and a bunch of higher end BMWs, Mercs, Lexus, etc. offering 400 hp or more, not to mention the insane offerings now at 500+ hp.

Doug

 

No switch on my 99. Just a stop with a quarter turn lock and slide up or down to adjust. I feel the increase in resistance as I near the end of the pedal travel this must be the kickdown.
I was looking at the cable adjustment under the bonnet mentioned at the beginning of this thread. No clip or zip tie on mine. In seems like Pedal is a little high compared to my other cars. The dead pedal for the left foot is a reach and is not comfortable in relation to my right foot. Ideally the throtle should be a bit farther away and the dead pedal a little closer. Last evening I installed an extension to get the dead pedal an inch closer and it has helped but not enough. With the seat all the way back and raised up about midway my right foot just isn't quite where I prefer it. I may try to adjust more free play to the accelerator cable therefore lowering the pedal. As long as I can lower the floor stop to hold the pedal at fully opened it shouldn't make any difference to the throtle body but may alow me to get more comfortable.
I'm just having loads of fun in my garage tinkering. Thanks again for the input.

 

First off, Merry Christmas and Happy Holidays!

I never noticed this thread until today--ended up adjusting the retaining clip two and one half revolutions. Very noticeable difference on the expressway on-ramp. (Chicago has too many entrances where you jockey with someone exiting right as you enter the highway and then need to get back up to speed to merge--so this will come in handy.)

Thank you!

Sabrina




1999 XK8

 

OK, so get this...


I have put the Puma away for the winter, but after seeing this post and watching Sam's video, I had to go look. Mine was ALL the way IN... Like beyond sloppy loose. So I pull the pin out, pull gently on the cable until it was snug and BAM. It moved 4 full notches!!! The factory marking paint wasn't even visible before but I can see it now!!! If the weather is good tomorrow, I may have to do a quick test run. It's funny, in the 3 years I've owned and loved this car, I've never thought it particularly fast. Would it not be SO funny to find that I've NEVER had better than 75% throttle????


Thanks SO much to everyone on this post!!! My already legendary love affair with this car may get even hotter tomorrow!!!

 

Napadsm1
As you have a 4.2 you also need to teach your ECU your pedal travel, see the earlier post #240 for the 4.2

 

I believe you can also make this adjustment in some cases by lowering the floor stop.
And pushing the pedal closer toward the floor board. After adjusting the free play in the cable under the bonnet, I checked the stop under the pedal, and it had a gap between the pedal that was closed before the adjustment.
If you don't adjust the floor stop, everytime you go to WFO you will be stressing the linkage as well as the cable. Simply bring the floor stop up to the bottom of the pedal, until you feel the tap of the pedal against the plastic stop.
Now the throtle is adjusted to the stops on both ends of the cable.

 

Greetings, I 1st read this post after purchase of my 1999 xk8 and checked it the same way I check a carburetor throttle adjustment. I would check it before making any adjustment. I have someone put the gas pedal to the floor and then I either pull back on the throttle on a carb or see if the throttle will pull back or the throttle body will turn any further on a fuel injection. When I check mine it passed the test and I called it good. Now that I read all the posts I had to go out and check it again and it passed I also hooked up my ODBC 2 reader and IPhone app and with engine off get 99% throttle open so Im calling it good. I am never at the last 1% anyway. I can see where this will help your car perform better if not adjust correctly this is nothing new and goes back to carbs but I wouldn't make any adjustment until you do the test. Oh and I might mention my xk8 has only 32k miles on it. Thanks

 

Ok. If you haven't tried this, TRY IT. I finally was able to take her for a ride today and I swear it is a different car. It spins faster and harder and shifts differently as well. I seriously believe that I've never had full throttle in the 3 years I've owned this car, so I never knew what it could really do. I'm in love all over again

 

Dear god. I was not expecting this. Not at all. The car has come alive.

Before I had 63% throttle when mashing the pedal. I finally figured out how to do so on my car, which is different to everyone else's for some reason, and now that I have 100% again, I feel like it's a different beast.

The XK8 can be plenty scary to drive. I'm starting to think I have never crashed this car because of that 37% deficit in WOT. Before, I wasn't even able to engage kick down when mashing the pedal.

I guess I'll hold off on wanting to upgrade to an R. The 8 is possibly too fast for me. I'll have to readjust to driving it.

Maybe it was the guy driving it, but my 8 smoked a brand new Ford Focus ST after this adjustment. (That's the performance model, quite fast.) The guy looked at me incredulous at the next red light. He asked me if I was flooring it, I told him, not quite. He was even more surprised. He then looked at me and said. "Your car is too quiet for its performance and engine." I've got to admit, his car made a lovely noise and at least sounded more powerful.

I can't imagine what its like to WOT a properly sorted R. I haven't really mashed the pedal in anything more powerful than my car, even though I've driven more powerful cars under parental supervision.

 

On my car, a 2000 XK8 the adjustment is done as so:

1. Get a friend to mash the throttle and then check for slack.
2. Remove screws circled in red.
3. Spin the tab that holds the throttle cable around the metal sheath (yellow) until you tighten the slack. It's like spinning a bolt on a screw.
4. Retighten the bolts in red that were removed. You may notice that when tightening those bolts the throttle cable is tightened just a bit more. Make sure to check again the throttle position percentage at WOT. It is easy to remove too much slack.

 

I have got to admit it made a big difference in responsiveness. I have a 2005 XK8 and the throttle was stopping about 3/4 inch short. After making the adjustment I noticed a quicker response when accelerating and a difference in how the transmission shifts even in non-sport mode.

I made the adjustment at my sons house 4 hours from home and had a blast on the way home. My son lives in the mountains in Virginia next to West Virginia. I was on highway 80 or 81 which is about 20 miles of hairpins and switchbacks. One hard curve after another. You'll often see many exotics on the road. People seeing just what their cars will do.

I got in behind a Porche with one of the 2 seater Cadilac XLR's behind me and a Beamer behind him. Didnt get to scarry but we were all playing and having a good time. I did make a video of the road as I went down it once. I will post part of the video but it just doesnt have the same effect. You dont feel the nose dropping dips into sharpe hairpin banked curves with quick acceleration and braking inbetween.

 

This topic always fascinated me. I plug the scanner in once in a while, it shows 100% throttle. Let me ask rather than just assume: Can the scanner show throttle at 100% if this adjustment is loose and not actually providing WOT?

Thanks,

John

 

What he says below

The WHOLE procedure took me less than 5 minutes (including looking around for my mini tie-wraps) and I DEFINITELY can tell the difference. I don't ride my car hard very often (I have my sport bike for that), but I definitely can feel the improved throttle response

I underlined some of the KEY points below for emphasis...