Hey all,

I've had this issue with my B5 S4 for a little over a year now.  Besides this issue, the car runs flawlessly.  I have looked for assistance on other forums with no luck.  I've also gone through different tunes and ECU's and the problem remains the same. 

The problem:

Just as the title states, the car has an idle surge during rolling idle.  If I'm rolling slowly (1 - 15 MPH range) with the trans in neutral and clutch engaged, the idle will bounce up and down until the car comes to a complete stop.  Once stopped, the idle will smooth out and behave normally.

I have replaced some hardware here and there with no such luck.  I do not want to begin to throw parts at it again, hoping that something will fix it.

Can anyone help me? 

Adjusting torque reserves KFMRES and KFMRESK and getting your idle trims as close to 0 as possible with adjustments to KRKTE and TVUB, among other things will help get rid of this issue.  I had the same problem even on stock fueling and all, and I finally worked it out once going full stage 3 with fueling and all.

Thanks for the replies, guys.

I do think its a hardware problem as this issue began after performing some major services; in other words, there was no change to software.

I purchased the car from the previous owner as Vast Stage 2; the only aftermarket components were suspension, clutch, K&N Air Filter, downpipes and exhaust.  The issue did not exist when I first got the car.

It began directly after performing the following services:  timing service, all new coolant sensors, DarIntake mod, new OEM air filter, new spark plugs and power steering fluid flush.  The car was down for roughly 5 days before all of the aforementioned work was completed.

Once work was completed, my first "real" ride with the car was on the way to work.  As I was rolling slowly in traffic, I noticed the rpms were bouncing up and down.  Shortly after, the CEL came on.  Upon arriving home from work, I checked the codes and it was P0300 for random multiple misfires.

So, for over a year now, I have to hold down the clutch pedal while coming to a stop or rolling slowly in traffic.  If I don't, the revs will bounce, blocks 15 and 16 will show misfires counting and CEL will eventually come on; P0300 Random Misfires.

It's a very annoying issue and there's no other signs of a problem anywhere else.

I initially thought the same thing!!! But according to the PS System diagram in the Bentley manual, it's an entirely mechanical system.  I cannot find any electrical parts on the PS system.  I also thought there was a sensor that raised the idle.

Keeping the clutch pedal depressed raises the idle a little bit.  For some reason, this keeps the revs from bouncing.  I have no idea why it works.

EDIT:  I forgot there is a steering angle sensor, which is part of the clock spring I think.  That tells the ECU that the wheel is turned.

There are different maps for idle area torque reserves dependent on clutch position.

Phila: A lot of people with healthy cars experience this issue. I would bet there are many cases where the issue is software.

Phila, yeah you're right but I've seen this problem on more S4s than I can count.  Maybe what the op is describing is a different problem, mine was more of a studder when rolling very slowly around 4-5 mph and coming to a stop.  It also went away when throwing the clutch in.  And to be honest the injectors aren't the same after 150k or 200k miles of use.  Like I said I didn't even resolve the issue until going stage 3 fueling, but I can tell you that I was able to resolve it with tweaking idle reserve and getting the trims as close to 0 as possible.  Also making sure KFMIOP is stock values in the idle areas as well.


Another Note:  If you notice the OEM factory design of the spark plug, is a multi-ground strap plug.  If I was a betting man I'd say this helps with the misfire problems being experienced here.  Considering no one really runs these as they can't be gapped this may have something to do with it.

Phila, what's irresponsible about it?  Is it going to blow his motor if he increases his torque reserves? I think not.  Anyways, just sharing my information and what I've found and seen with my own and other people's cars.

TBH I thought the OP had fueling, and didn't even think about him being stock. It would be nice to figure out why so many s4's have this problem... I wonder if my theory on the single electrode vs multi ground strap oem plug has something to do with it.

More of a general philosophical issue, since so many hacks don't bother to fix their hardware before dicking around with maps they shouldn't have to...