Plugged in the scanner tonight to make sure everything looked good for inspection tomorrow and noticed that with key on, pedal to the floor TPS is showing 52% max...that can't be right. When I had the engine covers off a little while back I checked the cable at the throttle body and didnt seem like too much slack, but I'll definitely adjust tomorrow to see what I can get out of it. There's also a plastic "stopper" under the pedal that limits travel, but I assume that's a kick-down sensor of some sort. Any adjustment on those? Pedal seems to travel only an inch or two.

Car runs great and pulls decently hard through the rpm range for the most part, but obviously something's going on here. I'll start with the cable adjustment, but can't believe its only showing 52% at the moment, I'd think the car would feel pretty slow at WOT with a reading like that.

Guess my question would be, if adjusting the cable doesnt get me to 85%+ what else should I be looking at?

 

You should be able to reset it by winding the adjuster up to get closer to 95%+.

Then I'd carry out a hard reset, and let the ECM run the throttle plate adaptation, whereby it runs the engine thru high idle to almost stall point and settles back to running idle, somewhere between 550-650rpm.
Job done correctly.

 

I had similar but im convinced that was a plot by my prior owner.

Anyway, id make sure the kickdown switch is all the way down. On our cars, its just a quarter turn fastener, so just twist the button and push down, then twist back.

Will make a big difference in performance

 

Thank you guys, will take a look at it later. May adjust the throttle cable as well just to be sure. Had the car out this morning to get it inspected and put my foot all the way down and sure enough the car pulls really hard to 4k and then that's it, won't give any more. Guess I wasn't driving it hard enough to notice.

@Seanb - What is the correct procedure for a hard rest? Just disconnect the negative for 10-15 minutes, or disconnect both cables and touch them together? Can never remember.

 

Think it was done on purpose?

 

I do. I think he knew the car had head gasket issues, so to avoid getting too much boost, he wound the kick down switch out.

I first noticed when the car would not give me 2 downshifts even when i pushed the pedal all the way down.

Did some testing, did like 3 quarter turns on the engine bay adjuster and pushed down the kickdown. Now see about 98%, but its close to having the throttle be open at idle, so its a fine line.

 

Wow, that's messed up. Imagine what would have happened with that car had it not gone to mechanically inclined owner such as yourself. It would probably cost more than you paid for the whole car in shop fees to get it where you have it.

 

Oh I'm sure. Just hearing about the owner who paid almost $4k for timing chain tensioners made me realize that I could never afford "fancy" cars if i had to go to a shop. I also like to help out people who live near me, so open invite to any local jag owners.


Give those few things a try on your car, bet you'll find some free HP

 

Maybe we should give the previous owner a "Scarlet Letter" or something. When you find someone
who is willing to profit by deception techniques, it really provides a bad taste.

 

Yea, I saw that thread too. I couldnt afford to own one of these with regular shop bills either. I mean I could, but defintiely would not get any enjoyment out of it paying that much for service.

Working from home today and just went out to the garage to adjust the switch. I can push it down and turn left/right, but it always comes back to the same position. Not sure what's gonig on with it or if I'm doing something wrong. Obviously can't just keep twisting as the wire moves with the assembly.

 

so if you twist 1/4 or half turn, can't remember, and then push the thing all the way down and then twist again before releasing?

 

I'll give it a shot later when I have some more time. There's definitely movement there so I'll figure it out. Was just reading a few old threads and apparently this is fairly common. A few posters with early XJRs mentioned this exact issue and a night & day difference after adjustment. Hoping that's the case here.

 

It sure was for me. When at a decent rpm, the car felt pretty decent before when i was getting 60% throttle, but when I corrected this issue, the double downshift would result in some real power, more blower whine, etc. Was a very noticeable change.

 

That's great to hear. It's funny, I've thought this car felt a bit underpowered since I've owned it but I wasn't driving it too hard so didnt think much about it. Pulls great off the line and can hear the blower, but wasn't really winding it out and when I finally started to put my foot all the way down there was nothing there. I'll mess with it later and hopefully report back with some good news.

 

This has me feeling like I ought to check my kickdown as well. My car has plenty of power, but when I floor it and I feel the kickdown switch clock (I think) it doesn't seem to do anything at all...this is in normal mode, not sport. In sport it kicks down but still not as agressively as I imagined it would, Been meaning to check the switch to verify it works, I presume its just a 2 wire plug and it closes to engage so a simpe continuity test, right? Might as well check the throttle position at WOT too, see where I'm at.

 

Definitetly worth a check. I was shocked to see 52%! Hoping I can get this all fixed up later today, excited to see the difference.

I've been trying to remember how my 2003 XJR felt and I think it was similar to this car. Guess I just thought these were too heavy to actually be quick (and comparing to an 11 second GN warps your view on power at times), so wonder if that car had a stretched cable or kick-down issue as well.

 

Winding the kickdown switch out to sell a car? that is as low as it gets.

For those that want properly setup throttle - remember that these cars are fly by wire so it's important to use an OBD reader to get the 99%.
(I've found 100% can cause a warning light as the TPS v TPPS are out of range, anything around 95% is good).

A hard reset is removing battery terminals and have a cup of Java, then reconnect.

Next
​​​​​​plug the OBD reader in, key to ignition on, scroll to 'live data' and there should be a throttle setting.
Slowly depress the pedal and watch for a smooth rise in percentage, note the WOT maximum thru the kick down switch. If it needs adjusting then pop the hood, locate the adjuster and add tension a turn at a time, once in the 95%+ range zip tie the adjuster in place and start the car, let the ECM run throttle adaptation. Let it run up to temperature, it will fall back to 550rpm.

Next,
Find a quite open road and peel your wig back! A properly setup XJR is 0-60 in 5 seconds all day every day.

 

x308 are drive-by-wire? I assume since there is a mechanical connection between the pedal & throttle body via the cable they were just like any other old car.

When you reference the adjuster under the hood you're speaking of the cable adjustment at the throttle body, correct? I plan on doing that first regardless. Unless there's another adjustment under the hood that I'm not aware of.

 

4K rpm’s is considerably choked. Once you get it to open in the 90% range with sport mode on from a complete stop, you’d swear you were in another car. If you’re feeling really frisky, just turn off the traction control first then let er rip tater chip!

When you adjust the cable at the TB, there should only be a little bit of up and down play in it before the throttle blade moves.

 

That is the misconception - a cable connected to the TB. There's a motor that actuates the plate, not the cable and right foot. I've stripped a few of them down and the ECM, servo motor, throttle position sensor (TPS) and throttle pedal position sensor (TPPS) do the work. Your input thru the cable is then turned into an electronic signal they use & you can measure, doing by eye is not correct and can leave a very high idle.

Yes, the cable adjuster!
Hope this helps.