onedae

I have a new 2017 C4S with PDK. My first PDK - always had manuals in the past. I'm noticing a very slight hesitation when taking off in first gear from a dead stop. It feels almost like a stumble for a split second. Any thoughts?

neil.schneider

991.2? Turbo lag?

onedae

yes 991.2 but definitely not turbo lag.

Archimedes

What about it makes you think it's not turbo lag? Can you describe it?

Dennis C

It's normal for PDK, although it seems to be more noticeable in some cars than others. I experience the same thing with my 991.1 TTS. It's best to think of the PDK system as an automated manual transmission, as opposed to an automatic transmission with a torque converter. When you take off from a start, the PDK system has to engage the clutch, just like a manual transmission. It takes a fraction of a second to do this, and it feels like a slight lag or transmission slip. If you start your car in launch mode, you won't notice this behavior.

I thought I had a problem when I first experienced this too, and I have had multiple discussions with my Porsche dealer about it.

Jay-S

Are you in normal mode or sport? Normal seems to have more PDK-lag from a stop.

onedae

I'm never in normal mode. Generally in sport but occasionally in sport +. The slight hesitation is in either mode with moderate (not super aggressive) drive off. Dennis C - thanks for your explanation - sounds very reasonable.

Needsdecaf

Thank you for saving me from typing this. Perfect explanation.

mac10

well said. Which is also the same reason you should not keep a PDK car consistently(barely) moving in traffic with your foot on the gas pedal. Either on or off the gas-like a manual.

JR956678

A good description. Also consider that the PDK is programmed to emulate what happens in an automatic with a torque converter in that the car begins to creep as soon as you take your foot off the brake by partially engaging a clutch. You can notice this action - when at a dead stop with your foot on the brake the clutch is completely disengaged (to avoid wear). As soon as you take your foot off the brake you can see a slight change in idle speed and hear a change in engine sound as you put a alight load on the engine.

It may feel as though the clutch is slipping because it really is. As you apply throttle the clutch begins to slip less and less as the car is accelerated to higher speeds.

In Normal mode this action is rather gentle allowing slightly more clutch slippage to get a smooth transition to forward motion. In Sport or Sport+ the action is more aggressive. Sport and Sport+ seem to actually get smoother the more aggressive you are because they are performance oriented modes - being too "gentle" sometimes might feel like a hesitation though it's really just normal action of the PDK and the clutches.

Yes - there's no reason to put wear on the clutches by keeping them in this "slipping" mode for no reason - that would be sort of like "riding the clutch" in a completely manual gearbox. I would point out that the PDK and its clutches seem really robust - consider what launch mode puts them through with virtually no limits on how many times you can launch the car without activating a "limp mode".

onedae

Thanks for the responses - very helpful.

sechsgang

Sounds like standard PDK engagement to me. Unlikely a problem!

Madisongy

Same issue in my 2015 991S PDK. I've lived with the hesitation from stop for two years and started getting so fed up I'm am searching everywhere for an explanation. This simply cannot be right. And many folks indicate they do not get a lag. Dealer says "no warning light, can't help ya". I remember when mechanics could diagnose issues without a light, and there has got to be some of those guys around. Anyway, in the attached thread, Rainier and Jay-S indicate that they had the dealer perform an ECU update that "affected the PDK" and this cured the problem. Now these guys experienced the lag, so they know how the car feels with that, and their statements sound very convincing that the car no longer exhibits that behavior.
Just curious if anyone else has had any experience with this. I'll likely take the car over to these yokels again and ask them to check for any updates. (although my car is newer than when they had these updates performed and you'd figure they would be incorporated into the ECU already)

https://rennlist.com/forums/991/7641...m-start-9.html