Vac Leak or Bad Sensor???
Thread Starter
Drifting
Joined: Nov 2005
Posts: 1,745
Likes: 35
From: Turlock CA
Vac Leak or Bad Sensor???
On my 2016 Z06 A8 I am having an annoying and somewhat dangerous problem in that the car does not want to slow down when letting off the gas. In town it is very noticeable, especially in paddle mode when I downshift, expect the car to slow down, but instead it stays at the same speed or even accelerates a little. I also confirmed that it does this at high speed when I have downshifted to 4th or 3rd and it only slightly slows or again speeds up until it has gone far enough to finally lose speed. The only way to get it slowed down is to use the brakes.
I have considered that it maybe a vacuum leak but the idle is steady. I am thinking it may have something to do with the rev-matching or a sensor on the throttle-body. There aren't any codes shown.
I stopped by the dealer and took the tech for a ride and it showed him that even at slow speed (25-40) in first gear (paddle) letting off the gas slowed a bit and then blipped up in speed all without my foot on the gas pedal. They did a quick check and didn't see anything posted by GM and I will need to drop the car off for them to research it further. I plan to do that this week.
Before that, I wanted any learned advice on what it may be.
Thanks.
--Dan
I have considered that it maybe a vacuum leak but the idle is steady. I am thinking it may have something to do with the rev-matching or a sensor on the throttle-body. There aren't any codes shown.
I stopped by the dealer and took the tech for a ride and it showed him that even at slow speed (25-40) in first gear (paddle) letting off the gas slowed a bit and then blipped up in speed all without my foot on the gas pedal. They did a quick check and didn't see anything posted by GM and I will need to drop the car off for them to research it further. I plan to do that this week.
Before that, I wanted any learned advice on what it may be.
Thanks.
--Dan
Thread Starter
Drifting
Joined: Nov 2005
Posts: 1,745
Likes: 35
From: Turlock CA
Thread Starter
Drifting
Joined: Nov 2005
Posts: 1,745
Likes: 35
From: Turlock CA
Drifting
Joined: Apr 2008
Posts: 1,356
Likes: 105
From: Mesa AZ
Exactly! First rule in debug is start eliminating things, I.E. your mods. Start with the catch can (which it probably will be), if it isn't the can put the stock intake back in. In a long shot situation it could be the Afe if you have the gen 1 and the AFR is so far off its making you gain speed.
Thread Starter
Drifting
Joined: Nov 2005
Posts: 1,745
Likes: 35
From: Turlock CA
I'm just not sure. Car now has 880 miles on it and I wasn't paying close attention to it until I started to push it more and use the paddles. If left in auto mode it is tough to feel what's happening as it's always in a higher gear than if I was driving it normally.
I dropped it at the dealer this afternoon and we'll see what they find.
I dropped it at the dealer this afternoon and we'll see what they find.
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Thread Starter
Drifting
Joined: Nov 2005
Posts: 1,745
Likes: 35
From: Turlock CA
Exactly! First rule in debug is start eliminating things, I.E. your mods. Start with the catch can (which it probably will be), if it isn't the can put the stock intake back in. In a long shot situation it could be the Afe if you have the gen 1 and the AFR is so far off its making you gain speed.Are you familiar with the Elite can? Is there something in the vacuum line routing that could cause this?
Thanks.
Drifting
Joined: Apr 2008
Posts: 1,356
Likes: 105
From: Mesa AZ
It wouldn't be the airflow as much as the Fuel Trim percentage error that is created with that intake.
I do not have one on my C7 but all I know is there is a 10 million page thread in the Z06 section about people arguing about whether its needed, whether it causes problems..... Thats why I said start there because I know I have seen vacuum issue with it whether they were installer error or the device itself I am not sure.
Hopefully the dealer will be able to figure it out quickly.
Hopefully the dealer will be able to figure it out quickly.
Last edited by ktoonsez; Mar 22, 2016 at 11:30 PM.
Thread Starter
Drifting
Joined: Nov 2005
Posts: 1,745
Likes: 35
From: Turlock CA
Without too much effort they sent me home saying to put on more miles. The claim is that the A8 needs upwards of 2k miles to correctly learn its shift points.
I think it does have something to do with one of the mods and will pull one off at a time when I have the time and check to see what happens. It's not that I doubt what GM is saying but that so few, if any others, are having the same issue.
I'll look into the fuel trim as you suggested.
Thanks.
--Dan
I think it does have something to do with one of the mods and will pull one off at a time when I have the time and check to see what happens. It's not that I doubt what GM is saying but that so few, if any others, are having the same issue.
I'll look into the fuel trim as you suggested.
Thanks.
--Dan
Drifting
Joined: Apr 2008
Posts: 1,356
Likes: 105
From: Mesa AZ
Without too much effort they sent me home saying to put on more miles. The claim is that the A8 needs upwards of 2k miles to correctly learn its shift points.
I think it does have something to do with one of the mods and will pull one off at a time when I have the time and check to see what happens. It's not that I doubt what GM is saying but that so few, if any others, are having the same issue.
I'll look into the fuel trim as you suggested.
Thanks.
--Dan
I think it does have something to do with one of the mods and will pull one off at a time when I have the time and check to see what happens. It's not that I doubt what GM is saying but that so few, if any others, are having the same issue.
I'll look into the fuel trim as you suggested.
Thanks.
--Dan
Thread Starter
Drifting
Joined: Nov 2005
Posts: 1,745
Likes: 35
From: Turlock CA
No, I'm a total Mac user. I do have HPTuners on my Air laptop but have never attempted to look at LTFTs -- or know what they are. I used the software to mainly change parameters between street and race on my C6 but I have licensed my C7 to tune.