I have a 2002 XK8 with about 64,000 mi on it. Out of the blue with no prior warning signs it is now giving me problems. I replaced the battery just to eliminate that as a possibility so the battery is new and it was an expensive one. I replaced the TPS with another factory Denso one. I'm getting the p1251 and the p0122 codes. Before what was happening the car would go into restricted performance mode and that's when I changed the TPS. That didn't do any good no changes. I cleaned all the connectors and the MAF. Now when I go to start the car it immediately goes to redline wide open throttle. When I turn the key to on the butterfly does cycle open closed And then opens and stays wide open,and when I turn to key back off it cycles and closes completely. I unhook the TPS and now the car says fail safe mode but I can start it now in an idles at around 1100 so it doesn't go full red line. I am just at a loss. I'm thinking maybe tear the throttle body off and send it into that place that rebuilds them. Anybody have any thoughts. I was told Dale maybe able to help.

 

My car is a 2000 XK8 so we have the same fuel system. Car had numerous issues when I first got it. Sent the TB to ASI and that cleared things up for a while but it seems you have done what they do. I had two problems recently and one "restricted performance" issue was resolved by cleaning the MAF and the TB itself. Another problem I had was surging on acceleration but you dont seem to have that, it was the fuel filter. It you have checked all the electical connections I would look at the plastic breathers and the intake tube for leaks. Also I would just make sure the TB has not come loose or the gasket is missing. Also the big rubber gasket where the intake tube and TB meet. These are all long shots but easy to check. The TB does have some coolant hoses that run through it but you would see the leaks and unlikely they would cause your problems. It just seems like you have a leak somewhere is the system and the ECM is being confused.

 

I've checked everything nothing's cracked broker leaking. And all of those issues wouldn't cause the problem I'm having when I start the car it goes to right away red line. When I turn the key the butterfly cycle's open closed open closed but then it just stays open 100%.

 

Well I never had the WOT condition you describe. My GUESS would be either a bad TB or ECM. If you don't have a wiring diagarm to check the circuit then I believe you can find a copy on the preamble threads to this forum. I had my TB rebuilt by ASI and they seem pretty good if you think that is what you need. As far as getting the EMC reparid or a replacement I have not had to do that yet. Good luck.

 

You sent your TB and got yours back?

 

The engine in my car is the AJ27 4 liter which should be the same as your 2000. ASI will rebuild and return your TB if they can do it. They do give a warranty and will let you know if your TB is rebuildable. www.autoecu.com is their website

 

I saw some place a company sends you one already done and you send your for a core. Wonder if it's the same

 

While digging in I looked at the ASI website and they want now about $750 to rebuild your TB. Having mine done was half the price. It is interesting that on eBay they offer the position sensor and the position module for $350. Also on eBay are remanufactured ones from China for around $450. Plus there are always the ones from salvage yards. If you have all ready replaced the TPS I wonder if the ECM is a more likely cause of your issues A Workshop manual could be useful in diagosing the issue based on the OBD codes you are getting.

 

Were these codes also present before you changed the TPS?

 

The JAAAG has been down for two months. I got the throttle Body rebuilt,,,,All is well in the world again. Runs perfect.