I made a fast decision today and would like some affirmation/validation if possible. Either way what's done is done, but I would still appreciate feedback.

Last week at gas pump after pumping gas I started my XJR and it went into engine failsafe mode. P1121 and P1222. Immediate restart and it went away, drove 60 more miles with no problem. Drove about 30 miles today and while it was back in the garage still purring smoothly I pushed the window up switch and it went into failsafe mode again. This time only P1121. In between those two times I disconnected and cleaned all electrical connections to the throttle body.

The MAF and O2 sensors seem to be in sync because my fuel trims are extremely good. I think that leaves the TPS as the most likely suspect.

I just paid ASI to rebuild the throttle body that's on my shelf from my previous XJR (2003). I guess I will ship it to them tomorrow but I have already placed the order.

Impetuous of me?

 

Perhaps not impetuous. My XJR has suffered from the dreaded failsafe during its life. The current throttle body I have on the car is nearly brand new and on occasion the fault still occurs. Disconnecting the electrical connection between the TPS and the TB itself and cleaning/bending the contacts has never failed to get me going again. I have just received electrical components to bypass the awful connector assembly and built my own hardwired into the TB and the TPS connector under the hood.

Having your TB rebuilt seems like a premature decision from my perspective, unaware of your entire situation. I have a feeling that the true cause of the endless failures I go through (and others too) are electrically based and not a hardware malfunction. I do stand to be corrected though, of course.

Here's to hoping your rebuild in fact solves the failures.
Q

 

Cleaning the contacts and using some dielectric grease would be my first choice.

 

Thanks,
As I stated I thoroughly cleaned the contacts after the first occurrence. I can keep investigating the cause since the throttle body I am sending out is my spare.

The rebuild is fairly inexpensive, too. Even if I just store or sell the rebuilt one it was not prohibitively expensive.

 

+1 what RJ said. That dielectric grease is good stuff for preventative situations. When I recently rebuilt the engine in my wife's recently acquired 1990 300ZX, I replaced about 90% of all sensors, cleaned and greased the other 10% and hasn't been an issue since.

Having a ready to go TB isn't foolish anyways. Even if you ended up selling the car, you could always sell the TB and make your money back.

 

Have to agree that having a spare ready to go can't hurt. I'm in the same boat, tried everything but the TB rebuild, just haven't been able to find a way to afford the downtime, since it's my daily. Let us know how it goes though.

 

I have dielectric grease on my shelf but it appeared the little rubber seals were good so I didn't apply any. It's been very hot and very dry here so I would not expect a moisture problem to be the culprit. Not even dew because she's in the garage at night. But the dielectric grease is surely a good insurance against moisture. I have accidentally gotten that stuff on the metal prongs before and it causes problems!

I did spray CRC electrical cleaner on the connection points before I plugged them back up.

I agree that it's very possible the throttle body does not need to be rebuilt. I think that since so many potential faults have been eliminated on this car I was quick to try and nip this problem in the bud! I've had a hankering to send the spare one off to rebuild anyway and this gave me a ready excuse.

We'll see...

 

Spare throttle body is at ASI being re-built.

In the meantime I have tried pumping the accelerator slowly through its full range while the ignition is "on" but car not started. Did it ten times then went for a drive, no problems. Did it 10-15 times before each of the next 3 starts. Still no problems or codes.

Certainly not conclusive, but it appears there may be potentiometer corrosion?

 

They turned it around in just a few days. It looks cleaned up and nice. The next time my car throws the p1121 code maybe I'll swap it out. The code hasn't come back since I have been cycling the accelerator occasionally just before starting the car.

I was under the impression they sourced potentiometers (sp?) and replaced the Denso ones that came from the factory. On the phone the ASI tech told me the original design was faulty and they installed an improved version. It appears though that the potentiometer has the same faded Denso label on it as before. I will contact them of course to better understand what they did, but if any of you are familiar with how they re-build and can shed some light I would appreciate it. I bought the 2 year warranty with it so I'm not too worried; just curious.

 

It's possible they replace a component inside the potentiometer, rather than the entire thing.

Why did you have to purchase a two year warranty though? I thought they already came with a lifetime warranty?

 

When I placed the order it offered a lifetime warranty for $100 and a 2 year warranty for $40. I hope I didn't misunderstand and buy something I didn't need.

 

It's been a couple of years since I ordered my rebuilt unit, maybe they've changed their offer

 

Jeff, the 1121 will probably get worse, so you haven't bought something for nothing, I've a couple of spare TB's because of this issue - you probably stumbled on my posts on this code while researching yours. The TPPS is the other one which is internal.

 

I'm sure you are right Sean. I'm glad to have the re-built one ready to go but I can't bring myself to install it right now. I have a new EGR valve, new evap valve, new Bosch upper O2 sensors and now a newly re-built Throttle body on the shelf. But, I can't bring myself to install them. It runs and drives wonderful with fuel trims that are essentially perfect. I hate to start wrenching on a car that drives so great.

All of those "new" parts came off my parts car and were installed only a couple of thousand miles before the accident. I put them on my shelf because, having just bought them, I knew they were essentially brand new.

It's been about 5 drives and 300 miles in the car since I had any codes come up. I almost hope to see the P1121 again so I can justify working on an otherwise perfectly running car.

I have been pricing new leather for the drivers seat so I may focus on that while I wait for a sign regarding the Throttle Body.

 

It's about 3,000 miles later and the throttle body has not even hiccuped since I started pumping the accelerator before starting every once in a while. I still have the rebuilt TB wrapped in plastic shrink-wrap on the shelf.

I never drove a brand new XJR, so is it possible there would be a performance improvement that I don't even know is missing if I install the rebuilt TB even though the old one isn't giving me any problems?

I drive it to work about twice a month just to keep the battery charged. Yesterday was one of those days and it got me thinking "Jag" stuff again. lol I do love that car.

 

I noticed my TB codes disappeared as soon as the cooler weather hit me up here. Unfortunately for me, the cycling the throttle pedal had no effect when it was getting there. It's on my Spring To-Do list though, to get it sent and rebuilt as soon as I get a backup vehicle. The thought of trying to tackle another summer where it will constantly trip on any given day gives me a headache lol.

My guess is that you wouldn't really notice that much of a difference. Unless the one you're using right now is COMPLETELY gunked up to where flow is severely impeded, I can't see a fresh one being any more than a negligible difference. I'm sure there'd be some, just not sure how noticeable.

 

The early T bodies did have a problem .. and the connector as well--- the later units don't suffer from either problem. The connectors on the later cars should not fail in any greater number vs any other car .. and that = almost 0.

Having two XJR's and being around many more we really can't nail down a direct fault except when the TPS fails completely ---- pumping the throttle on a regular basis to clean the internal contacts of the sensor and keeping a newish battery seems to be the answer.

I did not know ASI did the R's t-body .. it is different.

Did you ever find out what they do / did to your unit ?

 

Since the TPS looked like the same old one that was on the unit when I shipped it off to be re-built I asked them about their procedure regarding that item. This was their response:

"Our remanufactured Throttle Position Sensors and pedal switches are entirely gone through, We dismantle the sensors and replace the internal parts that tend wear over time."

It looks like grandell was right.

 

Ok, so the hot/humid weather is back and so is the fail-safe mode. This time only P1222 though. I still have the rebuilt throttle body on the shelf in shrink wrap that I bought last Summer. I guess when the car is cooled off this evening I'll finally install it. Pumping the accelerator occasionally worked all Winter, but not so much now.

Wish me luck...

 

Last night turned into "family game night and then family movie & ice cream night" so I didn't swap out the throttle body yet. I am going to do it today but I'd like another opinion on something I'm considering while I'm doing that.

Also on my shelf I have a brand new EGR valve (with new gaskets), a brand new evap purge valve and 2 brand new Bosch upstream O2 sensors. My current LTFT are between +5 and +9 depending on my driving (I suspect a small leak at the throttle body gasket but I'll be putting a new one on today).

Question: While I have the throttle body out, should I just replace all of that other stuff, too? I mean, why not, right? Is it better to leave well enough alone and wait until something fails?

These items came off my parts car and I call them "brand new" because they had less than 4,000 miles on them between installation and the car being wrecked.

Thanks in advance for your feedback.