2005 S-type 4.2 jerks on hard acceleration
 

I have had this car about two weeks now and noticed that if you accelerate from a stop with full throttle the car jerks strongly. I think it might be the traction control, but I have never felt a traction control system cut off the engine so much. I tried turning off the traction control with the panel switch but it still jerks. Any ideas?

2004 XJ8 Hard "jerk" with aggressive holeshot
 

I can relate. My 2004 XJ8 has done this. It makes me cringe to think of risking serious drivetrain injury if I need to nail it in order to jump out there. I thought it might have been a loose surface/traction control override, but whatever it is, I don't like it. I also feel a little slop in the drivetrain when hitting it (in 1st) after a slow roll to stop or near-stop. It feels like the trans is not hooking up soon enough, but instead connects after the engine has spun a bit (too fast), risking shearing something off? Has anyone else felt this?

Naturally, we'd like to see codes but there could be issues that won't throw them..."just yet". Have you run your cat in a heavy rain or car wash? Moisture that finds it way into engine and trans. electrical connectors will cause the shudder described. Snoop around a bit and/or let her sit to dry out.

Make sure which of traction control or misfires it is. If TC maybe something about suspension/tires is wrong but if misfires then really hunt for why. Those kinds of misfires struggle to throw codes.

Read up on 'the lurch' transmission issue first. Very common and never completely taken care of by the factory as far as I'm concerned. :icon_hyper:

Follow up
 

So far there are no codes. I will check again in a few days. No I havn't got anything wet that I know of. I have read about the transmission "lurch" on earlier models, but the symptoms don't sound the same, everything works perfectly in normal driving. It is only under full throttle acceleration from a stop or very low speed that it happens. It seems to me like an overly aggressive traction control.

And yet your description sounds exactly like a really bad case of 'the lurch'. The DSC will not interfere unless one or both wheels rotate at an excessively high rate of speed as compared to the others. Even then, it only backs off the timing/throttle and in an extreme case applies the brakes in sufficient measure to tame the spinning wheel into partial submission. This is all accompanied by a flashing DSC light.

None of this will happen on dry pavement unless you've managed to break a tire loose and are 'burning rubber'. Go see your dealer and make sure you have the latest software version.

"The Lurch"
 

Isn't the "Lurch" a condition evident when coming to a stop the trans. doesn't downshift quick enough into 1st before stopping and accelerating again? Check your O2 sensors, particularly the upstream's. Poor O2 signal can cause a lack of power and shudder under hard acceleration.

At least on my car, it was most evident when laying heavily into the gas after coming to a quick stop. The BANG! sounded like all six speeds were going end up in my lap and the shock felt like the car had been rear ended. YOW! I stopped lending the car to people for that reason.

The dealer did the usual software update and it's now much more subdued but I have also adjusted my driving style to compensate. There was an excellent post somewhere on the board describing a test ride with a ZF engineer who could induce the lurch at will. Must be in the archives somewhere.

Have you noticed the lurch much more subdued in "Sport" mode?

Well...... not on the STR :) :)

Throttle lag? Really? Does the 3.0 have it or I wonder if you have a fault that's surfacing as that?

What are your car's fuel trims at idle and 2500rpm (in P will do)?

If you're asking me, the answer is no. Makes no difference. It all comes down to driving style to either provoke or avoid the problem.

Oh yea, if you hammer down from any position, most notable from a stop, I can almost count the (short of a) second it takes for the vehicle to react. Light throttle the rpm's raise a bit before the stall kicks in and locks the TQ converter. Feels a bit like my 2800 stall on the truck. (Not to that extreme of course, more like a 1400 if I had to guess) I'm just curious as to what the stall is on this trans.

I'll check the fuel trims and get back to you. Car runs great, idles smooth, rev’s under load smooth. I do notice that at about 3500-4000 feels like the powerband really comes in, (form of Variable timing, or Variable intake??) Thx in advance.

Maybe it's just what the 3.0 does.

IMT / VIS (intake/inlet manifold tuning / variable intake/inlet system)
It has VVT, too, as I recall.

Sorry for Reviving
 

Did you guys ever find a solution? Mine is doing this as well. No check engine light. New transmission. Idle fine.

Happens when I step on the throttle on the downshift, feels like someone kicked the car in the rear and the wheel slips the locks for a second. Really dumbfounded here.

Thanks for replying.

I'll take it to the dealership this week and see if I can get it flashed. How did you get it fixed, or did it just go away?

you will need the latest software update and also adaptions reset

this is how you retrain the adaptions as i stated previously .
you need to take it easy , with no full throttle , no kick down , and no sport mode , for around 400miles.

Ahh okay. Would you recommend a hard reset first? I just got the car back about two weeks ago and I've driven it in sport mode, etc.

​​​​​​Will it still reset the adaptions If I just drive it gently for the next 400 miles after being driven in sport mode, etc.?

Really appreciate your help!
Lately I've been thinking its the valve body and was looking at picking up a RevMax unit. I hope I don't have to do that.