Today was headed out to dinner and about 2mi out the 99 xk8 went into restricted performance, transmission fault, traction control failure. Shut the car down and installed my portable code reader and got P1121 & P1642. At this time I had a rough idle noticed the tack went to “0” and had a 3 or 4 beeps I think from the shifter. Attempted to clear the codes and restart but the codes did not clear and it still idled rough like a misfire and would not rev.

Going to connect my IDS tomorrow and see if I can get additional codes or direction. Just as I side note it has a new battery but will check it again. *On 3 other occasions not consecutively I had a rough idle on start and would clear itself moments after start. I thought it might be the fuel pump but now I am not sure that it is. I am now thinking ECM or ??. Could use a little serious input!

Note: *The 3 poor idle was on a hot engine after it had been shut down and sitting for about an hour.

 

Today the morning after the breakdown I got the car in the shop and wanted to read all the codes with IDS and this is what I got
U2012. B1858, P1000, P1121, P1642, U1261, P1797 & P1632.

I cleared all but the P1121 it would not clear. I charged the battery because it was down to 12.2 and wanted a full charge. I got it up to 13.0. I restarted the car and it had a wavering idle and the TB was not responding. With IDS these are the codes that came back.

P1121 remained, U2012, B1948, P1632. With the engine running voltage was 14.0V so the charging is working.

What I am seeing is that the TB or ECM or both are having an issue. I have another TB that I can put on but do not know how good it is but the fact that the P1632 - ECM code is up I am thinking ECM trouble.

I will be replacing the TB to see what takes place.

 

Fixed!! It was the throttle body. Used an old TB i had on the shelf. Now to get the other one rebuilt AGAIN!

 

Glad you got it sorted and thanks for the update. Certainly better than an ECM!

 

Just curious. Do you think your code P1121 points to bad pedal position sensor on your throttle body?

 

Well I was not sure. I was looking at that but the ECM codes threw me. I had the TB and thought I would give it a try and it worked.

As a side note the P1121 & P1632 did not clear so I took the chance on the P1121. That PPS is what the ECM is looking at and I felt if the PPS has failed then the ECM could not see it. It could have been the other way around. It was a gamble I took in replacing the TB. Not everyone has the luxury of having one on the shelf like I did so it would have been an added expense had it been wrong.

Thanks for the offer to loan a TB.

 

When you send your throttle body to ASI will they tell you what the problem was or do you have to ask for the diagnosis. It would be nice to know what is wrong with your throttle body that way later down the road we might be able to help diagnose other cars that had your symptoms.

 

I was thinking about asking. I would like to have a better understanding of what took place and why. I should note this TB has been repaired by ASI once in 2014. That is a short life on that repair.

 

They could of repaired only what was wrong with it last time, TPS or something else, and didn't do anything to the PPS because it was working at the time they did the repair.

 

True! I did think about that but I have a habit of saving all my transactions on both cars and that TB was in for a P1121 code. Will see what they say about it.

 

Those other codes like U2012 & B1948 are odd. I don't see how the TB could cause them.

 

The U2012 is ABS and the B1948 is Climate Control. Next project! I was actual going to start working on the roof system, interior and rust but this came up. Hope to get on them soon.

 

Such "fun"! Let us know how it goes.