Starting a couple of months ago, I started getting the lovely limp mode - ABS failure, Trac failure, Engine failure, etc... mainly on wet, cold days and shortly after starting from cold - within a mile or 2 from my starting point. It seemed to be preceeded each time by undue, almost dangerous modulation of the throttle. No codes were thrown, no CE light and it would reset by shutting down and restarting after 5 seconds or so.

First two occurences were about a almost 2 months apart, and then they started getting closer and closer together starting last Thursday until this Sunday when finally they were occuring every couple of minutes and it finally threw a code - P0121.

I traced that to a bad TPS signal, pored over the electrical diagrams and this forum, found all the references to TPS connection pin problems and found that it indeed has the tin pins. Cleaned all pins with contact cleaner/lube and reassembled and it all went away. I'll find the gold pins and replace them, but for now, this seems to have taken care of it.

Okay, so that's all good. Now the strange part - after the repair, and after about 20 miles of driving, I got one limp mode again - preceeded by a loud and hard THUMP while driving at 70mph... this time the same errors - ABS, Trac, etc... but also Gearbox - explaining that THUMP? No code thrown. Shut down and restart and it was fine again. Driven 100 miles since with nothing.

I had the tranny rebuilt about 1500 miles ago and this is the first time I've had this fault since. SO, has anyone experienced a similar fault - the THUMP at speed followed by limp mode? Anyone have any insight into it? I'm going to put it down to a bad CAN message that, perhaps caused the tranny to try to downshift, until the ECU caught the error.... unless it happens again. Tranny appears to be operating normally again, no change from before.

As an intersting aside, I got this XJ8 from my father 3 months ago, after the tranny failed - he didn't want to put any more money into it. It was serviced religiously at the local San Diego Jag dealer - who, coincidentally, just closed its doors in December. Before they closed, I got them to print out all the service records on the car. Turns out that about 1.5 years ago, they replaced the throttle body, charging him about $2500 for the job. I just came to find out the other day that replacement was supposed to be covered (free) by a TSB that extended warranty on the TB until December of 09... WTH? And, of course, they didn't replace the tin TPS connector contacts with gold as also mandated in the TSB. Dang, if they were still in business, I'd be in their face in an instant - charging the poor old man $2500 for a warranty job and then not even doing the whole job.

Can anyone think of any recourse to getting some satisfaction out of this? They're gone... but the parent company (Penske) still exists and has several other 'quality car' dealerships here, just not Jag. I sure would like to get some of that $2500 returned to my dad, 85, retired and living on his pension.

 

Has anybody had the hard BUMP followed by limp mode?

 

I had a '00 XK8 that, when called upon to downshift from 5th/Converter Lock to 4th, would produce a loud and seemingly damaging BUMP. Since the transmission was a recent dealer warranty replacement that sorta left the TCM. Not willing to spend over $2000 to see if that was the problem I learned to drive around it by backing off the throttle and manually downshifting. A few months later I was able to find a used TCM for less than $100 and sure enough, that fixed it.

Apparently, the TCM was not directing the torque converter to unlock when the downshift was called for. Sorta like shifting a manual transmission without using the clutch. Never set a code or went into limp though.

 

I'd consider this as a possibility, but it's only happened this one time - driving at 70 on flat, smooth highway, and it did cause the typical total computer wacko response with all the failure modes + limp.

If it happens again (I'm knocking on wood that it doesn't) I'll start looking at the TCM for issues.

Any brillliant ideas on the throttle body ripofff by the dealer?

 

Still hoping that someone may have had a similar transient - a hard BUMP followed by limp mode, reset by shut down, no problems since.