It has been nearly 2 years now since my car (08 MR) was badly destroyed and repaired. I noticed shortly after that every once in a while when slowing down to 1st then accelerating, the car will appear to hit the breaks on me for a short burst, often causing my seat belt to lock from the jolt.

I am not driving it hard, this is a very casual acceleration out of 1st (for example slowing down for a turn and then taking the turn will often cause this).

Recently, it started happening nearly every time. I have brought it to the dealer multiple times but I always get the "cannot reproduce". I plan to bring it once again as one time there was a near rear-ending due to a close follower and how off guard i was caught by the jolt. Hopefully I will be able to get it to happen on a drive with a dealer rep in the car.

Any ideas what is going on?

 

I don't know if you are talking about the same thing... but I have experienced a jolt when slowing down and then picking up speed rapidly again.

Let's say I'm slowing down... and the car is going down thru the gears. If I accelerate firm again as the car is shifting from 2 to 1... the car will have a jolt as if it didn't know exactly what to do at that moment. I just ease up on the throttle for a split second and get on it again.

 

well like i said I am not picking speed back up rapidly, these will happen at very slow speeds while driving through a parking lot or taking turns.

Also forgot to mention, it makes a banging noise when it happens. Sounds and feels like I am running into a wall. First time it happened I swore I hit something or someone hit me from behind. I have had passengers in the car when this has happened who have thought I actually randomly hit the break myself, so I know its not just me just over-exaggerating.

 

i get pushed back into my seat when i let on and off throttle in 1st gear, if ur in traffic and u speed up a bit then let off, speed let off it tries to go 1-2-1-2 so the banging is the gears

 

Why is the car trying to shift for me when I am in control? This happens both in auto mode and whatever the other shifting mode is called.

It really shouldn't be struggling to figure out which gear to go into when I am making a slow acceleration out of first. I am not going from one extreme to another, this is a very casual slow down and proceed type of change.

 

Well technically the car will still downshift no matter what mode you are in to prevent it from stalling.

 

This is a known behavior of the transmission. When you are slowing down and then quickly transition to the accelerator the TCU is trying to determine what are your intentions, and determines that it needs to be in first gear to acton those. When it does downshift, it does not seem to have rev matched properly, and the result is heavy engine braking. I have pretty much gotten rid of this behavior by one of two things- driving in Sport mode (auto or manual) or (and this is the biggie) by getting into the gas while the car is still going straight- before you go into the turn. If you transition to the gas in the turn, you can almost always reproduce the behavior.

 

I understand it still downshifts, that is not the problem. I downshift it to 1st as I have slowed down, then begin to pull forward. The car breaks when I start a steady and constant acceleration, not when it slows down. I begin picking up speed, then bam, a sudden break out of no where as if the car thinks I am hit from behind? I dont get it. There should not be any question of intent or downshifting as the car is still in 1st!

So the solution is if I ever go down to first gear I have a ~10% chance of banging gears unless i come to a complete stop prior to continuing? I find it hard to believe the car is that trashy.

 

You don't need to stop... just be smooth. It only happens to me if I accelerate while it's in the process of switching from 2 to 1. If it's already in 2 or 1 I don't get that "BANG".

 

You guys are really missing the point. The car is brought down to 1st, and I stay at first for about 3 seconds slowing down to a crawl (taking a turn, "crawling" through a stop sign"), and then as I begin to drive again STILL IN 1st, it happens. No shift from 1-2, all while still in 1st gear.

 

Do you have a Tactrix cable? Sounds like some logging would be in order to help understand what inputs are confusing the car. Might want to look into those who are doing the SST tuning to see if they can give you an idea of which items to log to get started...

BTW, are you _untuned_ at this point? If so, put your stock intake back on and drive it around for a few days to see if that doesn't improve the situation. Any lights or indicators coming at you from the dash?

 

my car is a week old and ive already noticed this.. ive resorted to just using manual mode. seems to take out alot of the choppy behaviors. the milage meter also seems happier in manual. by keeping the revs out of the boost. that said.. ive only got 1640km on it so far. and trying to be easy on it..