Surging idle when brake pressed down

[MidnightTSI]

So I've searched and found people with similar problems but none like mine.

When I press the brake pedal down the idle jumps from 900 rpm's to 1500 rpm's. If I keep the pedal depressed the idle will come back down. If I pump the brake rapidly the rpm's will stay at approximately 1550 rpm's constantly.

The idle is also inconsistent without pushing the brake. Sometimes it will be smooth, and sometimes it will surge a few hundred rpm's. A lot of you guys know how this can be extremely annoying (especially with a 3" exhaust with no cat).

The car runs fine while cruising and is perfect at WOT. No problems anywhere else besides idle. Fuel pressure is also very consistent at idle but I think my next step will be to upgrade my feed line and the stock fuel filter.

I checked my grounds, my brake booster vacuum cable, and my idle screw. They all seem fine. I have done a BLT and my system holds pressure very well. I can actually wait a few minutes and take the BLT'r off and still have a few PSI. My mods are up to date and I'm just looking for some insight on this. Thanks in advance guys I'm pretty clueless at this point

I will post up a video sometime in the near future if I can't get this resolved.

 

[nlzn]

While this isn't a solution if your IACV is going out it could cause this.

When you press the brake pedal the rpms will fall ever so slightly. The IACV responds to the small drop but instead over compensates. Now you have surge. It senses too much fuel from the attempt to raise the idle then cuts it. Then it sees too little fuel and adds it. Circle of idle hell.

Just for kicks unplug your IAC and nail the brake pedal and see what happens.

 

[MidnightTSI]

Thanks for the help nlzn.

I forgot to mention that my IAC is deleted with a blockoff plate.

I'm going to make sure I don't have any vacuum leaks today and play with the BISS screw a little bit. I also found a great thread on idle adjustment for others to reference.

http://www.dsmtuners.com/forums/bolt-tech/286287-iac-fiav-delete-still-idle-surges.html

 

[jstgon]

Could it be a possible grounding issue?

 

[MidnightTSI]

Could it be a possible grounding issue?

I've checked all of the grounds and they seem fine.

I am doing some work on the car today so I will give you guys an update. Thanks for the help.

 

[MidnightTSI]

So I black RTV'd my BISS screw just to be safe as stated by Twicks69 (Wiseman) here: http://www.dsmtuners.com/forums/bolt-tech/286287-iac-fiav-delete-still-idle-surges.html

I also cut off the vacuum hose ports on the top of the TB and JB welded them closed. I think this looks much cleaner than having the rubber caps all over the place. I don't trust those at all.

I then let everything dry for about 8 hours.
I started the car and it began surging again. I lowered the BISS screw to around 650 RPM's or so and it stopped surging
I stepped on the brake and it didn't jump. If I pumped the brake really fast it would jump a little but not a whole lot.
I also brought the RPM's up fast and once they came back down it would steady itself out immediately at 650
It seems as if it is resolved but we will see when I drive it tomorrow in 110 degree heat

The car was running for about 10 minutes with a perfect idle the whole time. My DSM has never done this before!