Now what?! TPS? Stuck pedal? Vid inside
 

ok so, finally get the car to start and stay lit... but the idle is going up and down. I figured AAV, but by dumb luck found the pedal seems to be sticky. If I bring it all the way back it idles up and down. If I just touch it it idles fine but too high. If I go to the throttle stand and twist the throttle all the way shut it starts idling weird again and only gets set a little open again if the pedal is touched....even with the pedal sticking there's no reason for the idle to pulse... is the TPS bad? I set it a month ago


https://streamable.com/ebzz8

Look for some sort of binding in the linkages or cable. Perhaps the notorious throttle bushings? Perhaps disconnecting the cable will help isolate things.

Also there's a bushing at the pivot point of the throttle pedal. Worth taking a peek at it

The idle surge is almost certainly too much air coming in....from somewhere. When the RPM reached xxx-level the ECU cuts off the fuel and the idle momentarily drops. Repeat, repeat......

On principles make sure both throttle blades are set to .002", the throttle bores are clean, and the linkage is synchronized.

Cheers
DD

Sticky thing is bound to be mechanical but depending whether fitted to your car the idle switch might also be worth checking in regard to uneven idle.

i an almost certain the linkages are not set to a high standard. I did a vacuum test last week and it was low... hunting vacuum leaks is the worst. I'm tempted to take it for a spin as is to see how it acts but I'm afraid it will quit a couple blocks from home.

What model XJS

Up to about 92/93 the cruise control pulled on the accelerator pedal via an arm mounted on the pedal assembly. Mine catches slightly and holds the throttle open.

88'

im thinking the bushings are bad as I do know there is a lot of play in the rods. I feel like the balljoints on the rods are crap too. Can a person just buy the balljoints?

those rods are used in radio controlled models. Something like this.

https://www.aliexpress.com/item/10PC...06.4.10.j1eTeO

Possible, I reckon, but I've never seen any that caused a problem, personally. They will obviously wear a bit over time but the rod adjustments can compensate for that.

Does the movement not feel smooth?

Cheers
DD

yeah it's not smooth feeling. The bushings are crap. I took this pic last night... this is the amount of play https://cimg3.ibsrv.net/gimg/www.jag...cb0aa1535c.jpg
before the butterfly's start to move.

You can adjust that play out. There is backlash in the whole setup.

Remove the links from the throttle bodys and adjust the butterfly's with everything disconnected, put the links back on the TB's. Then remove one of those rods and adjust the other one to take up all the slack, remove it install the other one and do the same. Put them both back on.

Lastly check both butterfly's open simultaneously and you're done.

yeah I've got some new bushings coming. Then I'm going to adjust the butterfly's. I haven't tried to put a "feeler" gauge in but they look almost fully closed to me but I guess it's pretty hard to see a .03mm gap. I'm new to jag and new to v12s. I can't believe how finicky something like slightly uneven throttle bodies can make it run a bit off. Also I have the coolant sensor coming so hopefully that will get it running properly. Also need to track down the vacuum leak... ugh might just make a homemade smoke machine tester

Are your sensors toast? in the video the first thing I saw was oil pressure at MAX and your car is overheating at idle?

Here you go.

They were posted a long time back, maybe you missed them.

Attachment 202299

Attachment 202300

yeah the dash is all messed up

Cool thanks... one thing, why a 2mm spacer against the stop?

Dunno.

Never gave it any thought, the factory manual says so, and that was waaaaay before the Internet was invented, and we did as we were told, and worked out the errors later if needed, and I have stuck with that procedure.

Grants spacer suggestion ensures that both throttles are synchronized, but have sufficient action to fully close against the throttle stops.

This is to ensure the ham-fisted do not set the rods so the throttles are held open by the rods/capstan system, but, once the spacers are removed, are properly against the throttle body stops, with a tiny bit of free play on the rods system, including a bit of play in case of thermal expansion of the rods etc when the heat gets into the engine.

Spot on.

The manual does mention that, but its just habit now for me, same as the LH and RH threaded rods. Seen a few of them snapped due to the lack of thought of the spanner man, and the manual does not tell you that one.

V12's are so special, just like most owners.

Greg, this is a very important point! Before following Grant's method I had a high idle after having driven long enough to really heat things up under the hood. IIRC When I did the math ( I was bored ) I came up with .4mm expansion in the rods from ambient to full hot engine bay. My rods were snug with no rotation of the capstan and, sure enough, it raised idle when hot. When I went in to set them via Grant's 2mm spacer method I took note, and it gives the rod just about .4mm slack. I prefer to think someone had their slide rule out rather than that it was by chance.