I've got two issues which may be related, so I thought I'd put them in the same thread.

A few months ago, after only having put the car in manual mode once before, I decided I'd give it a try. I rounded a corner at low speed (less than 20, worthy of 1st gear) in auto, then held the stick to the left until it switched and mashed the gas pedal. The car blasted forward with a ton of power for about a foot, then it felt as if I had hit the brakes hard, then slammed me back against the seat again, and then felt like the brakes again. It jerked like this about three times, with me in a panic, before I let off the gas entirely, put it back in auto, and then it drove normally again.

A month or two after this, I got the courage to try manual again. I drove out of my neighborhood, making a large slow curve to get into the left-going traffic lane, dropped it in manual, mashed the gas pedal, and it rocketed up to 60, shifting at redline just like I expected it to. I wrote off my prior experience as a fluke, and put it out of my mind.

About a month ago, I felt like doing some "spirited driving", so I made a slow curve into the left-going lane, slapped the stick into manual, pressed the gas a little bit, and it started to jerk again. Not with full-throttle power like the first time, because I only had the gas down a little bit. I let up on the gas, switched it into auto, and said "I'm not doing this anymore".

That brings us to this morning. I was on my way to work, driving in my neighborhood with a 25mph speed limit. I was driving like a civil person - a grandma, even. I came to a stop sign, and stopped. I pressed the gas a little bit, just a little, and for a second I thought it was doing the jerking thing, in auto this time - but I don't think so. It send me forward with more power than I had intended, and then forward progress momentarily stopped.

But then I realized my traction control light was blinking at me while progress had stopped momentarily, and after driving forward regularly for a few feet I looked in my mirror and saw tire tracks which may or may not have been mine (not sure). I know this car has a lot of power, but I wasn't even at half throttle, the roads weren't wet, I don't have any mods, and I've only got like 150 miles on my brand new set of Nitto Invos!

What's going on here? I know the car "learns" how you drive, did it suddenly decide that I don't drive like a grandma, and went into drag racer mode?

 

That is acting 100% normal. Grandmother Mercedes WILL NOT allow you to create too many lateral G's (yaw) without engaging the Electronic Stability Program and/or the Brake Assist System.

It takes torque off when it senses wheel spin or side-sliding.

Try doing this with the ESP/BAS disabled-it will act like most other cars.

 

Sounds like the traction control doing its thing to me. See if the jerkiness goes away when driving without the t/c on. If my tires are cold when first driving, the car will spin the tires at part throttle.

 

exactly what i was thinking... my tires spin at partial throttle when cold...

and since you said you were on your way to work, i would assume there were fairly cold still.

 

Thanks for the input everyone. I had only been driving for a few minutes, so I suppose it would be fair to call the tires "cold" (Florida cold - 80F outside).

I'm glad I didn't take it to the dealer for this! I'll turn off the nanny and see how it behaves.

Thanks again!

 

Sounds normal to me....traction control doin what it's supposed to do....is the car equipped with a sprint booster ? Could be the reason for the half throttle launch ??? Just a thought !

 

try turning off the t/c traction control, Woody

 

I agree with everyone above. Also I have noticed when in autostick, throttle appears more sensitive. I can sit in second gear, give it gas, it will respond quickly and lurch forward. Your body gets pushed back, your natural reaction is to pull yourself forward. Well, you end up hitting gas pedal again. Hence lurching forward again. Just a thought. My wife hates when I do that.

 

Could it have something to do with the torque converter locking in auto stick mode? I know you can get some engine braking effect if you downshift with the auto stick. I can get the car to lurch forward and backward at slow speeds if I am not smooth with the throttle.

Maybe it's not the torque converter, but some mechanism seems to link the engine to the tranny the way a straight drive does. My Dodge diesel automatic does a similar thing in the tow/haul mode.