2001 XJR, 170k miles.

Have been living with throttle body issues (or what I assumed are TB issues) more or less since I bought the car about 2 yr ago. Started with occasional failsafe mode issues on the highway that I addressed by restarting the car and as the frequency of the issues increased, so did my frustration. Finally decided to buy the repair service from ASI last January, had it sorted by February finally. Since then I have had basically the same thing happen, first very occasional failsafe mode with P1121 and the frequency of these issues increased to the point where I've tried cleaning and hard resetting enough and I think its warranty time. Got the TB sent out to ASI, they got it last Monday, had it in the mail back to me Friday, I received it Monday of this week and installed it Tuesday. Seems to be the same TB, the TPS seems to have been replaced as the ASI warranty sticker has a different serial number on it and the screws are in better shape than the ones it had on it. I can't tell if the PPS has been opened up and repaired or not.

So I get this on my car, everything is connected and I set the TPS in more or less the same position I had the old one in some photos I took before it left. Followed ASI's instructions to turn the car on but not to start, let it sit on for 60 seconds, then start it. Car coughed, sputtered and died, second start it caught, seemed like it was misfiring, but there are no codes indicating a misfire. It smoothed out after a minute and was running more or less at a normal idle, though a bit fast at around 750rpm. Shut it down, tried to adjust the TPS back a bit and restarted, idle is around 630-640 rpm now, so more or less what I think is spot on. But it still runs like hell. I've got a knocking sound, which might be the my supercharger coupling, and I'll be able to eliminate by removing the belt, but I do know there is a bit of slack in the supercharger pulley. I've got restricted performance essentially on all the time now and I do have a code for the A bank knock sensor, which I'm hopeful is a ghost that will disappear when I get back to it tomorrow evening.

When its running and I step on the gas pedal and monitor the throttle position, I'm seeing what looks like steady progression in the %, but around 20-25% throttle it gaks and goes to 10% throttle and I get failsafe mode. I want to eliminate my work in connecting and adjusting the TPS and pedal cable slack before I call ASI and start hollering that they made it worse. Is there an actual procedure for adjusting the TPS to OEM specs? Ditto the PPS. I know enough about how to do the process, but is it just trial and error until I get it to show me at or near 100% WOT with the pedal floored and kickdown switch depressed? At idle how much slack should there be in the cable, or should there be any? I've got a tiny bit of deflection in the cable now and the PPS is fully retracted against its stop when the car is just sitting, but I've got myself convinced that getting the TPS properly dialed in first is my main problem.

When I first removed the original TB, the retaining thing on the 4 pin PPS plug on the car side snapped off, just old plastic. I secured it with a zip tie and it hasn't previously given me trouble (or could be the source of ALL my problems I suppose), but while I'm sure I'm making good contact there, I'd like to replace the end with a new one, does anyone know what the connector is called and I assume I need some kind of tool to release the conductors as well.

Possibly useful information and other work done
:
While I was waiting for the TB I decided to address some deferred maintenance, so I now have a new power steering pump installed, new upper bump stops on the front shocks and the one thing that I could see might have affected anything around the TB area, a new upper left O2 sensor, the installation of which was a bit of a bear, but I think made considerably easier without a TB in the way. I've been careful to recheck my work in the areas I've been in, everything seems to be tight and everything I disconnected is now reconnected. Had some smoke as the quart of PB blaster I soaked the left cat in evaporated...kind of hoping that I somehow managed to disrupt the plug for the A knock sensor, but thats probably too much to hope for. I suppose if the knock sensor is actually bad I could attach a new one to the side somewhere as I've seen in other posts here until I remove the supercharger...is there a test for it? Measure the resistance across the terminals?

Any thoughts on any of this? Things others have run into and disturbed while doing any of these other jobs?

 

“I've got restricted performance essentially on all the time now and I do have a code for the A bank knock sensor, which I'm hopeful is a ghost that will disappear when I get back to it tomorrow evening.”

Because I can relate with you on the TB madness and the rabbit holes that it poses, let’s take a break for a moment from the TB and focus on the above statement. Having read everything but in the back of my mind I hyper focused on the knock sensor. I had a customers 00’ XKR come in recently and I replaced a lot of the cooling hoses including under the blower. After I had the top of the block stripped off and cleaned, I checked the ohms of both knock sensors while they were accessible. The D/S KS read 200k ohms and the P/S read 190k ohms. The P/S KS when I was ohming it out, I noticed it took an unusually long time to get up to 190k. Perhaps 15-20 seconds. The D/S got up to 200k almost immediately. The car had no driveability issues or codes for the KS. I know many years ago a brand new OEM Jaguar KS was 202k ohms right out of the packaging. You need to unplug both of your KS’s and ohm them out. At a minimum they should both be around 200k ohms. If the A bank KS is a lot lower (or higher) than the B bank KS, you need to replace that sensor. If your KS is malfunctioning, it will certainly put it in RP and mess with driveability. You could get a new KS, plug it into the main harness on the A bank, wrap it up in a shop towel and temporarily secure it to a coolant hose. Clear all the codes out and drive it. At a minimum, you need to rule that new KS out if it fixes your RP or not. At some point you’ll probably want to replace both of those KS’s as it’s of course a pita to replace just one let alone two.

 

Thanks A2B, I was assuming the KS was tripping the restricted performance, but you're right in that its smart to troubleshoot it.

Are the two KS connectors the ones right under the front left of the supercharger? Near the part load breather?

 

Yes, they’re each mounted on a metal bracket forward of the intercoolers. 2 pin connector.

 

Bingo! 133k ohms after about 20 seconds or so on the right side, left side is 201k ohm instantly.

I'll order one up and connect it and see if I get different results.

 

Grabbed a KS from rockauto, ought to be here Monday. Figure I'll see about the supercharger coupler making the knocking noise so I can eliminate worry about that symptom.

Might fiddle with the PPS tension and TPS positioning to see if I can keep it from going into failsafe mode when I step on the throttle too...mainly because I have time on the weekend and I'm impatient to drive my car again.

 

Pulled the supercharger belt off and started it yesterday. The knocking was gone so I'll assume it's the coupler for the time being. Pulls is a bit iffy so I'll have to locate a replacement and order one up.
Noticed I was very wrong about the tension on the throttle cable, it was in fact holding the PPS off its end stop when at idle, so I loosened that up to where it's definitely at the full end stop, fired it up and still have both restricted performance and failsafe mode. I'll wait till the new KS is here to try again as I don't know if the bad one will cause both messages or just the restricted performance message. Car ran pretty rough though, actually threw a code for the B KS as well, so I might not have gotten the connector properly reconnected.

 

That knock sensor plays an important part in the engine control system. If it's not working correctly, the car control system is very off balance and there are many issues associated with the failure. I'd expect that many of the weird codes and rough running symptoms will vanish once you get it installed. Of course, you will need to remove the SC to get to these on a SC car!
Best to you and the car!

 

Mayhem, when you do pull the blower off, I’d highly recommend replacing both knock sensors, both heater hoses, plastic 3 way tee, bypass hose behind the aluminum water pipe, large o ring under aluminum base, both water pipe o rings, the brass quick connect vacuum port under the throttle body. Trust me, you’ll never want to go there again. Also use nothing but the original spring loaded Eaton coupler as every other solid one makes it sound like rocks in the blower. You can also replace just the pulleys for any of those belt tensioners.

 

Well the good news, new KS has silenced that particular code, bad news is I'm still going into restricted mode when I power on the car (key on, no start).
is there a guide on dialing in the PPS and TPS? Still throwing code P1121, I can clear it and it comes back in a few seconds. I'm thinking the throttle body wasn't repaired properly, but I'm hoping to eliminate anything else i can.

 

A2B, thanks for the list of things to replace when the supercharger is pulled, that's very helpful and I'll be saving that for a later date.

 

So a bit more detail now that I'm in front a keyboard and not my phone.

As soon as I power on the car and it does its self-tests, it goes into failsafe mode. The PPS makes its whining noise for just a moment and as soon as it goes failsafe it stops making sound. I was able to reset the MIL, PPS makes noise for maybe 1 sec and then goes right back into failsafe mode. I tried adjust the cable length so that the PPS is not against its stop and has just a smidge of tension on the cable holing it slightly open, reset the codes and it worked until I started moving it. I tried repeating this with making small adjustment after adjustment to the positioning of the TPS and it just doesn't want to cooperate. I'm struggling to find anything that could be causing this apart from the PPS in the throttle body that I just got back from repair is now actually worse off than it was before I sent it out.

Any suggestions for things to look at that might cause this kind of behavior outside of the throttle body itself? I've been looking for loose wires or connectors, exposed wires, maybe something got too close to the exhaust and got overheated or when the TB coolant lines dribbled around maybe some connector got wet...so far I've found nothing.

Been toying with buying an EBay TB and dropping it in to see if it just works, or at least gives me a different problem, which would at least still point me at the throttle body.

Going to give ASI a jingle and see if I can talk them into swapping the throttle body with one on their shelves. I'm convincing myself that the PPS is the problem here.

Any other ideas though?

 

Any AJ27 TB will work but you will need to swap AIR ASSISTED INJECTION for the blanking plate on the SC engine if you use a NA TB.

 

Thanks Motorcarman.

ASI says send it back in again and I'll do that. Keeping my eyes open for an AJ27 throttle body for not too much money. If anyone has one they want to part with, especially if its operational, please send me a PM. I think between the original one and this repaired one, the TB has been about 75% of the trouble I've had with my car...probably can't hurt to keep a spare.

 

I've done that myself, you need to swap the throttle cable bracket too.