I have rebuilt the throttle body on my 2000 XK8 2 times. replaced the sensor once. After each rebuild the car runs for a week or 2 then right back with the Failsafe which eventually will not clear. Code P0121 and only Code P0121 over and over. This usually occurs within the first few minutes then not again all day. (except on one occasion)

 

Computer issues possible in 2000 folks?

 

Have you checked the plug to see if the TSB has been performed? See if this helps.

Link JagRepair.com - Jaguar Repair Information Resource

 

Have you watched this video? It shows what he had to do after having his throttle body re-built and still having the P0121 Code. At the end he talks about the Check Engine Light going off after about ten starts, he does not mention performing a hard-reset after the final adjustment, or following the battery re-connect procedure to skip over some of the adjustments the car has to make after a reset, such as kick down, WOT, etc. I hope this helps you get your TB sorted.

 

03XKR: yes I have watched the video you attached. I have actually re-built the throttle body once. Ran for a Week. Then did a full reprogram procedure. Ran for a Week. Sent in a new blank and re-built a different throttle body. Ran for 2 weeks. Always code P0121. I never had the problems the video guy had with idle. Now the car is in the garage un-clearable as far as the codes. I wonder if this guys car ran 2 weeks later.

 

Gus: I have not. I was not aware of a plug TSB. I will look into it. I am not near the car now. The service records make no mention of the Gold Plug replacement. (I think that is what you are talking about) I hope that is it.

 

You can *try* plugging in and unplugging the barrel connector Gus is referring to 10 times or so and see if there is improvement.

 

dsnyder586: The gold-plated connector looks like a reasonably priced part. I think I will go ahead and order it.

 

The barrel plug is not the issue it is the one below it.

 

If you look at the wiring going to the TPS and you see tape in it the new leads were probably done. When you check that plug use caution they become brittle with the heat and the stay often comes apart. If your stay is broken that would cause the plug to move and that also could be part of the problem. Just use caution if you pull it off. Also do not pull on the wires!!

 

Gus: The heat embrittlement makes sense. I am getting the new part. I do not recall any splicing on the current plug wires. I really hope this fixes the problem. I have the car all tuned up, new tires, suspension set really well. I just need it to run now.

 

Hi.

I agree with what Gus has said, but in addition I would do the following:

Unplug carefully all plugs at the throttle body, spray sparsely with electrical cleaner (not WD40) and plug back in.

At the ECM unplug very, very careful, spray and reconnect. Be careful. This connector has an awful number of tiny pins.

In the engine management fusebox switch the throttle motor supply relay with another one of the same type. The relays seldom fail, but their connector pins corrode. Spray here also.

As your problem is coming back despite a rebuilt throttlebody, I would suspect a bad connection or a chafing wire.

ALWAYS DISCONNECT BATTERY WHEN WORKING ON ELECTRICS.

 

The issue seems to be fixed. I believe I had multiple problems. The throttle body did need to be rebuilt. This took the problem from being every day to once a month or so. Then I did the fix that Gus suggested Tech Service Bulletin 303-58 with the gold plated wires. (you have to buy 4 of them) I have not had a Throttle position code since. My mechanic may try Plating the connectors with gold solder on his next one to save some money. Thanks Gus

 

I had my throttle body replaced but continued to have problems. My mechanic sent both computers to be rebuilt. Ever since then the car has never ran better.

 

If the TPS plug is cracked (or if you don't want to shell out for the gold connectors), there is a Toyota part that works. I did the gold connectors first, but the plug itself was in too bad of shape, I ended up splicing in the Toyota part (with the intention of replacing the contacts with gold ones), but ended up just leaving the stock Toyota part. I also had a rebuilt TPS to go with it, and my problems were cured.

Here is the part info:

Designed Fitment: Toyota or Geo Prizm
Brand:Standard Motor Products
Manufacturer Part Number:RPCTH151
Interchange Part Number:213-446, 213930
Other Part Number:89452-33010, 94853125
Other Part Numbers:1985003011, 89452-06010, 89452-12050, 89452-22090

 

My wife has an 02 XK8 that has been coding P0121 off and on sore several months. The issue typically happens when she is stuck in traffic (idling). The plugs look fine and but have been cleaned to be safe. I removed the TB this evening to send to ASI tomorrow for a rebuild. I am hopeful that this will clear up the failsafe issues.

BTW...Does the 02 model have the TPS plug issue or is the gold connector fix for earlier models?

Thanks,
Jamie

 

http://jagrepair.com/images/TSB/XK8/303-58.pdf


The link above is for the Tech Service Bulletin for the gold plated connections. It is dated Nov 02. According to the bulletin the affected years are 1999-2001.
For other readers of this post. It has been 2 months and still no Throttle Body codes.

 

Ok I had good luck all summer until now. Last weekend I had the P0121 error again. Does anyone have any other ideas?
I have done the following:
Rebuilt the Throttle body.
Rebuilt the throttle body again.
Performed TSB 303-58 with the Gold connections.

Any other suggestions that have helped anyone Long Term would be welcome.

 

Disconnect the battery, remove both the throttle position and peddle position sensor plugs. Clean both ends with CRC contact cleaner apply a thin coat of dielectric grease and put the plugs back on. Do a herd reset then turn the key on for 5 seconds then off then on for 5 seconds then start the car. The delay in the key on off is to prevent the engine from racing on start up to 2000rpm. Hope that works for you.

 

I would try a good-used part and swap out. You should be able to find an AJ27 throttle from a 1999 to 2002 XK or 1999 to 2003 XJ sedan. Salvage yards are likely full of them.

bob