W210 owners: shifting question - PeachParts Mercedes-Benz Forum

muleears · #1 11-29-2007, 07:34 AM

In my 98 W210 with 158K mi. I have a slight pause in accelerating when going from accelerator to brakes and quickly back to accelerator. If I have to slow down quickly (say from 55 to 35) then quickly accelerate there is a slight pause before the car begins to accelerate, maybe a half second. No jerk when it engages, no noises, no flare, it just won't accelerate for that split second. Granted this situation doesn't arise often but it has me worried.

Some history on the car. I purchased the car in August. Ugly divorce sale, wife had all the records and wouldn't give them up. When I got the car with 148K on the odo. I immediatly changed the oil and did a drain and fill with MB fluid on the tranny. Didn't drain the TC. I hadn't driven the car much before this was done so I don't know if it was pre-existing.

Is this just a quirk of the 5spd? Does it have something to do with the "fly by wire" accelerator? Or am I worrying over nothing?

KarTek · #2 11-29-2007, 07:53 AM

I think it's the turbo lag. Mine does the same thing and even falls on it's face a little with each shift. I'm working on a solution right now that should be cheap and effective... The best combination! Something else I did to reduce the percieved lag was to remove the unacceptable slack in the throttle cable where it attaches to the TPS under the hood. There was actually a loop of slack in the cable and I had to press the peddle a good inch before anything happened.

muleears · #3 11-29-2007, 08:14 AM

Those are good points. I did notice some slack in the accelerator cable the other day. Getting rid of that may be the ticket.

KarTek · #4 11-29-2007, 08:41 AM

Yeah, it felt like the car had 20 more HP. There's a lot to be said for proper response from the go pedal. This is also a common problem with 7.3l Powerstroke diesels which are also drive by wire. As a side job, I modify the TPS and accelerator pedals on these trucks for better feel and response. It also improves the coordination of shifts on manual trannys because there's no awkward delay.

muleears · #5 11-29-2007, 12:07 PM

I does it when I stop also. If I quickly go from brake to accelerator there is a slight pause. Doesn't feel like turbo lag, only lasts about a half second then everything is fine.

TMAllison · #6 11-29-2007, 12:58 PM

Sounds fairly normal. Its a NA engine when you get on the pedal until rpms raise and the turbo spools up.

JimSmith · #7 11-29-2007, 02:02 PM

This is pretty common. On mine, when I am going to do something like that, I downshift (typically to 3rd) before I get to the corner, use engine braking and the brakes and get back on it with the rpms still high enough to have boost available upon demand. Clears this issue right up. Jim

KarTek · #8 12-06-2007, 12:45 PM

I was making close observations of the shifting this morning and I detect what appears to be a slight, "pause/thump" when accelerating from a stop or when moving at a slow speed alternating between gentle power and coasting... Don't know if it's what you're experiencing.

TMAllison · #9 12-06-2007, 01:41 PM

Evan - Thumps and clunks means you should look at your rubber flex disks sooner rather tahn later.

You don't want to be sitting on top of the front one if/when it lets go.

KarTek · #10 12-06-2007, 02:57 PM

It's hard to communicate the subtlties of automotive noises and feelings over the net. It's more of a VERY soft, slip in the tranny followed immediately by a small nudge forward as if a clutch is at first partially engaged then fully engages.

All of this is very soft and completely noise free. I will look at the flex disks though as I have not yet been under the car since I've owned it. At least in the rear area other than replacing the shocks.

Parrot of Doom · #11 12-06-2007, 07:56 PM

When you press the brake pedal, the ECU stops pumping fuel into the engine. Could be that.

BioPOWER · #12 12-06-2007, 10:13 PM

Sounds like turbo lag.
The same thing happens on my TDI, but it's especially noticeable because it's stickshift. Letting off on the accelerator between shifts brings the turbo off boost, and it must spool up again before the engine can make any serious power. I love the VNT though, it brings the turbo online almost instantly...there's almost no lag.