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      02-12-2018, 12:14 PM   #1
dakarwu
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Is this a brake or engine issue?

This issue occurred 3 times over 2 months. I am on the brakes at a stop light and the car will suddenly jump. The car doesn't move but it feels like if u accidentally lift off the brakes and immediately step on the brakes.

I initially thought this might be a brake problem but could it be an engine issue with it jumping? I am on OEM brakes and rotors. The system says I need new brakes in 10k miles.

Another completely different issue that might be related? I drove off about maybe 1000 yards to a stop sign and the car was randomly reving with my foot on the brakes. I assume it's just the cold start but this was a one off experience.
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      02-12-2018, 07:48 PM   #2
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Is your car an automatic? "Randomly revving" while braking sounds like the car is just downshifting as you decelerate. Definitely post videos of these occurrences for further analysis if they happen again.
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      02-12-2018, 08:24 PM   #3
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I think we might need a clearer explanation how did the car “jump” but not move? Also with these cars if you let off the brakes at a stop it doesn’t creep forward so not sure what you’re describing and when you say randomly revving do you mean at a stop your idle is bouncing with your foot in the brake? Sounds like maybe a leak in the brake booster if I’m understanding it right
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      02-12-2018, 08:51 PM   #4
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i've had something similar happen to me. i came to a stop at a light and then a few seconds later after the car was completely stopped, it felt like the car behind me idled into me (but they didn't). i want to say it has something to do with the DCT. still switching gears or had a hiccup or something. i didn't investigate much... the car wasn't acting weird and this is a very rare occurrence.

i think sometimes with things like the dct where the computer is moving actual clutches, sometimes it makes a mistake and has to compensate, and we notice something weird happening when it is doing it's "fail safe" thing. i'm just guessing.
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      02-13-2018, 11:11 AM   #5
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Quote:
Originally Posted by roastbeef View Post
i've had something similar happen to me. i came to a stop at a light and then a few seconds later after the car was completely stopped, it felt like the car behind me idled into me (but they didn't). i want to say it has something to do with the DCT. still switching gears or had a hiccup or something. i didn't investigate much... the car wasn't acting weird and this is a very rare occurrence.

i think sometimes with things like the dct where the computer is moving actual clutches, sometimes it makes a mistake and has to compensate, and we notice something weird happening when it is doing it's "fail safe" thing. i'm just guessing.
Someone idling into me is exactly how it feels like. I guess since it happens rarely I shouldn't be too worried. It just gets pretty annoying because its super random and catches me by surprise.
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      02-13-2018, 11:14 AM   #6
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Originally Posted by EJT86 View Post
I think we might need a clearer explanation how did the car “jump” but not move? Also with these cars if you let off the brakes at a stop it doesn’t creep forward so not sure what you’re describing and when you say randomly revving do you mean at a stop your idle is bouncing with your foot in the brake? Sounds like maybe a leak in the brake booster if I’m understanding it right
The engine rev was while my foot was on the brake and completely stopped. It sounds like how the ICV acts on cold start but much louder. I assume since I didn't really let the cold start finish it could just be that.
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      02-13-2018, 11:18 AM   #7
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Quote:
Originally Posted by dakarwu View Post
The engine rev was while my foot was on the brake and completely stopped. It sounds like how the ICV acts on cold start but much louder. I assume since I didn't really let the cold start finish it could just be that.
thats been known to happen when theres a failing brake booster. a vacuum leak
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      02-13-2018, 03:59 PM   #8
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Quote:
Originally Posted by EJT86 View Post
Quote:
Originally Posted by dakarwu View Post
The engine rev was while my foot was on the brake and completely stopped. It sounds like how the ICV acts on cold start but much louder. I assume since I didn't really let the cold start finish it could just be that.
thats been known to happen when theres a failing brake booster. a vacuum leak
You know what... I can't remember the timeline between the two events, but it sounds like the op would describe it the same way I did and I did have the vacuum booster replaced under warranty.
When it takes a dump, you'll know it, limp mode, lots of lights... this might be what you have, op.
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      02-13-2018, 06:14 PM   #9
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Thanks for the insight. I'll take a look into the vacuum booster.
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