Around 1 out of 5 times I press the gas from a dead stop I have about a 1 second delay and then a sudden lunge.

The feeling is similar to riding with a teen in a manual shift car who isn't very good with the clutch and revs the engine a bit and pops it hard (minus the followup jerking back and forth).

Another way to describe the feeling would be to have a manual parking brake on, pressing the gas, and then rapidly releasing the brake.

Any clues? Worried that it indicates a transmission going bad though I have no other signs of slipping, bad shifting, or clunks going from P to R to D and back.

I know there was a software update for lunging issues but since this vehicle is 2005 and has 103k miles I would assume it must have that update already.

 

There are some issues with computer software needing updated, I think for 2 to 1 shifts being harsh. Also the valve body could be sticky or the solenoids on it could have problems.

You could check to make sure the throttle body isn't sticking. I'm not sure if a drive by wire throttle has this issue, but a know an old mechanical throttle will sometimes get stuck if dirty inside and then might pop free as you step on the pedal.

 

Depending on how old your LR3 is (I believe the release was in 08)- there is a software update for the tranny to make this better - my '08 is still jerky sometimes if I try to roll into the throttle without a full stop (down shift from 2>1)

 

I had the software updates, but it still did it occasionally. I changed the transmission fluid and filter and it helped. It's the lock up clutches in the torque converter. Not sure if that's the correct term.

 

Thanks for the tips. Looks like cleaning the throttle body is easy enough for me to do so I'll try that first. Gunked up throttle sounds a lot like how this feels when it finally releases and lunges.

 

There are two different issues. One is the infamous "lurch" that was fixed with a software update years ago. The second is just a delay in the throttle response. A poster on another forum told of a trick where you put the key in position II (I believe) and push the throttle down to the floor for 10 seconds (or something like that) and then turn the car off until it completely goes to sleep (2 minutes or so I believe). After that it's good to go. No more lag in throttle.

Sounds ridiculous, but I tried it and it worked!

 

Interesting. My LR3 lurched a couple of days ago when the dash said that it was -1 deg. f. I assumed that it was very cold and may have been related to a cold transmission/torque converter issue. It did it only once, and hasn't since. If it does it again, I'll try your instructions and see if it helps.

Thanks in advance!

 

I spoke to a reputable ZF re-builder about down and up shift issues on the 6hp26(LR v8 mission)

1st step according to him would be fresh lifeguard 6, filter and Valve body removal/cleaning, not internally but specifically the sensors on top of the mecatronic unit, they are magnetic speed sensors and he believes that metal particles from lack of service accumulate on sensors giving erroneous data. sounds weird but possible, I will be performing this as soon as my metal trans pan comes in, couple of weeks, bmw backorder :[ when it does get here I will drop the valve body and do a write up with part numbers and such.

 

I've just had a major service performed which included BG treatment and updating engine and transmission software. I no longer experience the lurching.