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Discussion Starter · #1 · (Edited)
Hello, P-members. I usually get the answer from here so forgive me asking another question.

My car is '15 BS with PDK with 9500kms on odometer. Recently I have felt my car sometimes hesitates to speed up when I hit the gas after coasting just like the cars with turbo engines. I took a good look at the tachometer while driving when I stop putting gas pedal and found that the RPM sometimes suddenly drops to 600-700 and stayed there just like the idling (My car usually maintains the RPM and slowly RPM lowers after I let go of the gas pedal).

Is this some kind of mechanism to save gas or some kind of a problem? I think the engine is supposed to maintain certain RPM to smoothly even in coasting.

Sorry about the sloppy explanation and description owing to my short vocabulary.

Thank you in advance.
 

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PDK has coasting feature. Here is a video for the 911 and would be the same for others
 

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It's supposed to be a gas saver, about which I could car less in my CS. I only drive it 6k miles a year or so, and drive it for fun, not to save fuel. My CS is a manual, but I always drive with the Auto Stop function turned off and the Sport mode turned on (along with the PSE). Have you tried to see if the AutoStop and Sport Mode functions make any difference? If you have Sport Chrono, my thought is you should be able to defeat that in Sport Plus mode for sure.
 

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It's supposed to be a gas saver, about which I could car less in my CS. I only drive it 6k miles a year or so, and drive it for fun, not to save fuel. My CS is a manual, but I always drive with the Auto Stop function turned off and the Sport mode turned on (along with the PSE). Have you tried to see if the AutoStop and Sport Mode functions make any difference? If you have Sport Chrono, my thought is you should be able to defeat that in Sport Plus mode for sure.
I'd estimate that 99% of Porsche owners agree with you, but then there's the US fleet standard mandates: 35 MPG for 2016 and an average fuel economy of 54.5 MPG for the 2025 model year. So every model will have to pitch in to meet that standard. Of course the only realistic way for car manufacturers to meet that standard is that they offer a large percentage of electric cars in 2025 .
 

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I'd estimate that 99% of Porsche owners agree with you, but then there's the US fleet standard mandates: 35 MPG for 2016 and an average fuel economy of 54.5 MPG for the 2025 model year. So every model will have to pitch in to meet that standard. Of course the only realistic way for car manufacturers to meet that standard is that they offer a large percentage of electric cars in 2025 .
Except the CAFE fines are a pittance. We all pay them in the price of the car and PAG, BMW, MB, etc doesn't seem to care. They care about EU fines because they are big. CAFE fines, not so much.
 

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Something to all that, definitely. My recollection is seeing a window sticker where a GT3 had a gas guzzler charge of $1000. What GT3 buyer would care about that? I wouldn't care on a GT4, if I could order one. I'm retired and using my Porsche maybe 6k miles/yr nowadays, So I could care less about fuel price or gas guzzler charge on a new one.
 

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Like others have said - it's the auto-coasting feature part of the start/stop technology. You might notice your engine turn off when you come to a stop light sometimes as well. This is perfectly normal.

If you do not want the car to do it, simply either hit the A button on the bottom right of the console or just (this is my preferred method) hit the sport button. This will disable auto start/stop automatically.
 

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Discussion Starter · #9 ·
As always I get the answer here on P-9.

Thank you so much.

My SA didn't know about this either. He should study more.

The difference is that here in the video clip " the PDK's engages the correct gear again within milli-seconds comfortably and smoothly" and I have felt hesitation.
 

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Discussion Starter · #10 ·
Wow, you have read my mind. I tried everything to find out why.

I ,today, disengaged the Auto Stop and Start function and it stopped hesitating. Since my wife is pregnant, whenever she is in the passenger seat, I have to drive like a chauffeur that I used more of Auto Stop/Start function that I realized some hesitation.

What I learned is when I am coasting with 600-700 RPM, even if I pull the left paddle (-), the PDK does not engage. I have to pull it twice.

I have less and less time to enjoy driving my 5-month-old BS. The life doesn't always pan out the way I want.
 

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Discussion Starter · #11 ·
Thank you for your kind answer.

This is my first Porsche after three Z4's (2.5i, 3.0 turbos respectively) that I did not know about this feature. When I asked my SA about this, he was clueless and asked me " Isn't it because the gear shifted to higher one?"

This site is like a Wikipedia for Porsche. A lot of members are omniscient about Porsche. I am glad I found this place.
 
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You have to pull twice because the first pull "activates" manual mode (assuming your gear lever is in D) and the second pull tells the car to shift gears.

Can you describe what you mean by hesitating? It will hesitate slightly as the engine picks up to rev match the speed your'e at, but the car shouldn't lurch or jolt when it re-engages the transmission.

Wow, you have read my mind. I tried everything to find out why.

I ,today, disengaged the Auto Stop and Start function and it stopped hesitating. Since my wife is pregnant, whenever she is in the passenger seat, I have to drive like a chauffeur that I used more of Auto Stop/Start function that I realized some hesitation.

What I learned is when I am coasting with 600-700 RPM, even if I pull the left paddle (-), the PDK does not engage. I have to pull it twice.

I have less and less time to enjoy driving my 5-month-old BS. The life doesn't always pan out the way I want.
 

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The coasting function is of course described in the manual.

I've never noticed a hesitation in picking up from a coast, but then if I've got it in coasting mode I'm not in that much of a hurry.

Is you A/C on? Having A/C on will usually speed up idle some, which might make the pick up less noticeable. We always have the A/C on. As noted you can always kill coast mode if you don't like it. The start/stop button does, any of the sport buttons will. I have to explicitly go to coast mode by putting it in D instead of M where it usually is.

Coast mode is the difference between about 23 and 28 mpg on a highway cruise.
 

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If you turn auto-stop off, it will stay off even after you start and stop the car. Turning auto-stop will disable the coast feature. The coast feature can actually help you go faster in certain situations due to no engine braking.
 

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Discussion Starter · #15 ·
You have to pull twice because the first pull "activates" manual mode (assuming your gear lever is in D) and the second pull tells the car to shift gears.

Can you describe what you mean by hesitating? It will hesitate slightly as the engine picks up to rev match the speed your'e at, but the car shouldn't lurch or jolt when it re-engages the transmission.
It feels like a turbo lag. I might be too sensitive.

I now know it has to do with auto stop and star function that i dont have any reason to be apprehensive.

Thank you.


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Discussion Starter · #16 ·
If you turn auto-stop off, it will stay off even after you start and stop the car. Turning auto-stop will disable the coast feature. The coast feature can actually help you go faster in certain situations due to no engine braking.
It felt like a turbo lag. It took a little more time to gain acceleration for me. I dont know why.

Thank you for you reply.


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It felt like a turbo lag. It took a little more time to gain acceleration for me. I dont know why.

Thank you for you reply.


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I know what he's talking about when he says hesitation. The speed doesn't pick up fast enough, but that's because you're in such a high gear and low rpm when you come off coasting the car feels slow and thus 'hesitant' to pick up speed until it knows to drop a few gears. That's the nature if the mapping non sport mode.
 

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Discussion Starter · #18 ·
I found this on the maual. Its called "gliding".


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