1998 XJR 234,000 miles. (Don't laugh) I performed a search of the forum and on Google.

So I finally get my car running and the car doesn't hardly want to rev past 1500 rpm's. Complete valve job, valves adjusted properly, new headgaskets, timing chains set perfectly. I turn the engine off (I hear the throttle body do the self test turning key on & off without the engine running, so I know it has power) and I pull the intake tube off. With the key on, my assistant floors the gas pedal and the butterfly valve hardly moves. The throttle linkage goes to about (90%) wide open throttle with the gas pedal still floored, but the butterfly is not wide open. If I had to guess how much it opens, I'm thinking 10%. I have taken out all the slack in the throttle cable. I believe the electric motor that opens the butterfly is weak OR the shaft bushing is gummed/binding up. I am very mechanically inclined and was wondering if the electric motor is rebuildable??

What are your thoughts?

 

Well, I'm speaking from a 2000 VDP, but can you manually open the butterfly with a screwdriver or your finger by pushing on the butterfly itself? Is it stiff or smooth? Your perception of a weak motor may be correct if it manually operates smoothly. Did you clean the throttle body (since you did so much other work)....the butterfly shaft could be gummed up in the body?
I saw one on eBay for $75, free shipping, just in case.

 

There are a lot of "bits and bytes" between the throttle pedal position and the throttle plate motor. On your AJ26, I believe I remember the literature describing a mechanical override to allow the throttle to open about as much as you describe. So, while your "weak motor " hypothesis might be true, I suspect the motor is not getting the signals to open further.
Are you in "Restricted Performance"? Any codes?

 

Highhorse:

I did push the butterfly open with my finger. There was what I thought to be a little bit of resistance while doing so. I was going to just let the engine run up to full operating temperature and see if the heat of the engine would somewhat free it up but, I'm contending with a fuel leak at the front of the fuel rails first. I may dismantle the butterfly and clean and lube all that out first.

Sparkenzap:

I hear you on that. I am not in Restricted Performance mode. I'm going to bring the Autologic home tonight to get some readings along with my DVOM and see if the electric motor gets full voltage. Do you think this correct??
C2A1470EK $370 online Jag dealer cost for a new throttle body. Terry's Jag.com $278.10 (new??)
I just don't believe that's true since these Jag TB's go for $2K+ maybe I'm looking at something else. What the difference between air assist and non air assisted? (Not that I have a choice)

 

I believe your resistance is from your motor and that should be good because that should mean your motor should be functional. I believe what Sparenzap is saying may be the issue...getting it the correct signal for it to function.
Though cleaning it cannot hurt......here's an old post for your reading pleasure regarding '98 throttle bodies. Post 5 by Bob Gauff has detailed pdf's for TSB's from Jaguar...https://www.jaguarforums.com/forum/x...y-parts-48449/

 

I reckon the difference between air assist vs non air assist is the difference between the AJ26 (yours) and the AJ27 engine's TB. Yep, those prices sound low.

As to the motor "getting full voltage", I am pretty sure the throttle plate motor is a stepper, so it would need to be diagnosed as such.

 

I repaired the fuel leak and was able to run the engine up to temp last night. I was quite pleased that the hotter it got, the more the butterfly opened. It'll open up about 90%, same as the TB linkage (or cam). One thing still going on... I have all the slack taken out of the throttle cable. With the gas pedal floored, the linkage on the TB is about 90% open (along with the butterfly). With my assistant flooring the gas pedal still, 90% throttle linkage opening, with my fingers I can move the linkage to 100% WOT. Given the mileage, do you think I have a stretched cable? Or is there something else that needs adjusting to achieve 100% opening?

As far as the butterfly sticking when cold, I'd really like to remove the rod that the butterfly goes into so that I can thoroughly clean out all gunk inside the bushings. However, I'm a little apprehensive given the age, mileage and overall delicacy of this component. Does anyone have any input on this??

 

So, addict, are you saying the throttle plate is opening without the engine running? That surprises me. I assume the OBD parameter for throttle position is the actual plate and not the pedal, so you could monitor that under different conditions to see what is going on.

 

When the engine is cold and not running, the throttle plate barely opens. When the engine is at full temp and not running, it will open up a lot. I pulled the TB off tonight and I'm going to take it into work tomorrow to see if I should take the butterfly out and clean & lube the shaft. Have you done one like that??

 

I just did mine when I did my primaries and I simply use TB cleaner, spraying lots, wiping off, spraying lots, wiping off until I was happy with it.

 

Well I finally decided to investigate the TB at work and I dismantled about 90% of it. The screws that hold the throttle blade in place are very and must have loctite on them. So I ditched that idea. Long story short, there are a total of 3 sealed roller bearings that are locked up almost solid. I decided to buy the 3 bearings thru McMaster Carr and should have them Saturday. I'll send another update when available.

 

Jag likes to use red locktite....as for the screws on the blade, they may be secured with age. Try some PB Blaster and let it soak in.

 

What I meant to say last night is that the throttle blade screws are very soft and they're peened on the other side. I essentially ruined one of the Phillips head screws and I passed on the other one. I had thought about spraying PB on it but, that would've been a last case scenario if I couldn't get the bearings out. I could also just use my reversible drill bits and maybe an ez out to replace it with another screw with loctite on it. I still have one bearing left to get out and may need to go the fore mentioned route.

 

Any idea what corroded the bearings? Maybe sitting out while the engine was apart? You weren't running water or methane injection, were you. I ask because that has never come up as a problem before. Lucky you!

 

There are two roller bearings on one side of the TB and one on the other. The two roller bearings on the D/S (USA car) were almost locked solid. Since the car is a 98' with 234K miles, I'm going to say that time, heat and miles on the TB are to be expected. I have a feeling that's why the engine lasted as long as it did because you couldn't open the throttle up very fast. Parts should be in by Monday I'll let you all know how it turned out.

Also a big no on anything injected inside this engine.

 

Well, I completely disassembled the throttle body (minus the throttle blade), carefully cleaned everything. I measured the seized bearings and ordered SKF bearings thru McMaster-Carr ($58 delivered for 3 bearings. I don't use cheap crap) I carefully reassembled and installed the throttle body
aaannnnndd It works flawlessly!
I ran it up to temp last night and revved it up to just under 3K rpm's in park with no lag. Much gratification knowing that I can fix things with essentially no information on this process. I can spend a few days doing almost nothing!
However, I hope that no damn "Restricted Performance" will be illustrated on my dash anytime soon. I have more things to do before I can go out and drive it. Wish me luck!

 

That's great news and good work....what's the next episode titled?

 

"Tying up loose ends"

I need to tighten up the P/S exhaust manifold. There were 3 loose fasteners on the P/S that I had forgot about.

Install the 2 loose entire firewall pieces, get the hood back on. Replace the receiver/dryer for the A/C system, then wash and dry along with test drive.

 

As all of you are still here, I better ask the question here than open a new thread.
I today ran through all of the Torque readings while on a nice late autumn drive.
I noticed that my throttle reading does not exceed ~70%, both during full acceleration, and also when the engine is off.
If I turn the throttle by hand on the TB, I can reach a full 100%, although the last 30% seem to have some lacking (which was indicated here as being part of the engine management, perhaps??).

So, do you guys remember your readings once the stuff was solved?
Mine has a minimum of 1.4%, and the mentioned ~70% (with all slack out of the cable).

Car is a 1998 XJ8, is like new, and runs perfect otherwise.
I drive the car as a classic, and it hardly sees more than 2.500 rpm, nor full throttle, but as a perfectionist, this will bother me from now on .
Thanks if any reply!

 

I don't remember my exact readings but I think I managed 92ish percent WOT with a fully warmed up engine with key on engine off. I'm fairly confident to say that they will never reach a full 100% WOT. I can't explain why that is, only speculate.

With what you're saying, I believe your problem exists under your throttle (gas) pedal. It's the transmission kick down switch to be exact. If not adjusted properly (which most aren't), it will not allow the throttle pedal to fully travel. Whatever you do... DO NOT just turn the switch by hand. What you need to do is pull the carpet back just above the throttle pedal. Your looking for a white connector with 2 wires on it. Unplug it. What you have to do is turn the kick down switch clockwise but also rotate that short harness along with it. Those 2 wires can be easily pulled out of the switch and you'll have to source another one. I know there's a procedure on exact specs but I'm going on memory here. For a properly set kick down switch, the throttle pedal has to make light contact with the switch at 85% and when you press down hard on the switch with the throttle, it should read somewhere in the 90% plus WOT range. These readings of course are with key on engine off. If I were you, I'd start with 2 full rotations clockwise and check your readings and go from there. You may have to go several more turns though.