Tightlines612

2018 S4 with 18,000 miles on it. Spend 4 hours on the highway each week and experience the following problem at least once if not 3-4 times on a 2 hour highway cruise. Occurs both with cruise control on and cruise control off.

It "feels" like engine power completely stops for a fraction of a second. RPMs do not budge but what I recently noticed is that the boost goes from 0 or 10% up to 50-75% for no reason at all. This does not happen when under acceleration but instead when cruising at a constant speed. Again, cruise control on or off. The problem seems to be getting more frequent and is concerning. I am completely confident this has nothing to do with my input (especially since it happens when cruise control is activated).

I have not brought this to the attention of my dealer due to the intermittent nature of the problem and my poor experience (not at this dealer) but with service techs and intermittent problems in the past. I notice this when it happens on a 2 hour drive and know that they will not experience the problem when trying to troubleshoot it.

I haven't spent much time on the forum since I picked the car up and do not know if anyone else has reported or solved the issue, or even if there is a service bulletin for it. Did a quick search without much luck.

Any help is much appreciated. I own my cars for 7-10 years and hate to think I have some drivetrain issue that I'll be wrestling with the dealer on even admitting exists.

TheFatArmadillo

I have a slightly different problem, but occurs in a similar fashion.

I’ll be driving on the freeway and all of a sudden the car will downshift to about 4500-5200 rpm and the boost will spike. It has occurred when using the cruise control and also while holding a steady speed. Mine is going into the dealer toward the end of the month for the 30k mile service and this is on the list.

I’ll be interested to hear what they say and try to remember to report back. I would definitely take it to the dealer and see if there are any updates that need to be applied as there seems to always be one available.

jondin2000

Honestly after over 30k miles on my car I'm convinced this cars have faulty transmissions

RickNY

My car does this on a specific downhill entrance ramp all the time

Glisse

Sounds like you have Intelligent Coasting enabled. If you don't like it, turn it off via MMI: Car/Driver Assist/Efficiency Assist/Intelligent Coasting - check or uncheck.

I strongly recommend people read the manual, this is not a VCR

RickNY

Is that a Europe or ROW thing? Because on my US model, that option does not exist nor is it mentioned anywhere in the manual.

Glisse

No idea, first I've heard of a B9 not having the coasting function:

Burrcold

Definitely not a US/Canada available spec.

Glisse

The OP doesn't list their location.

The coasting function is present on all cars. Whether Intelligent Coasting is there may depend on the options fitted, as it is part of Predictive Efficiency Assist and is using radar, cameras, GPS etc to determine when to engage and disengage coasting. It is more intrusive to the driving experience, and I have it turned off. Others really like it.

The behaviour being described in this thread reflects the behaviour of the coasting function when it switches off. Most people don't even know it's there, but some dislike it in certain situations. Here's one reviewer's comment:


Source: CarAdvice.com.au - S4 vs C43

Link to full review:
https://www.caradvice.com.au/531963/...an-comparison/


As Audi point out in their generic description of predictive efficiency assist, a slight touch of brakes or accelerator will stop the coasting function. This applies whether you have Intelligent Coasting or not. So for people who don't like when the car's systems decide to switch out of coasting mode, they can override this with the right foot whenever they want.

Source: Audi Technology Lexicon

RickNY

At any rate, the US-spec cars do not present the coasting option you described in the MMI.. For cars without ACC, the only option we have is to turn "Predictive Messages" on or off using Vehicle, Driver Assistance, Efficiency Assist -- there is just a checkbox there. Cars with ACC get an additional option for "Predictive Control" under Vehicle, Driver Assistance, Audi Adaptive Cruise Control, Predictive Control.

Predictive Messages -- "When adaptive cruise control is switched off, the predictive efficiency assist only provides notifications without controlled interventions"
Predictive Control (only cars with ACC) - "When adaptive cruise control is switched on, the system responds to upcoming situations automatically"