87 S4 Tii

i cannot get the car to idle low enough. Basically the car idles at 1000. It stays at 1000 for a while then goes down to 850, this is what I want, but not after 30 seconds of sitting. It’s almost like it has to get over a “hump”. I have checked for vac leaks with a smoke tester, there was a super tiny one on one of the pivot arms of the throttle body, so tiny that it hardly let smoke out. At the 1000rpm idle, the afr is 10, at the 850 idle, the afr is 12. At the 850 idle. If I turn the headlights on, the voltage starts to go from 14 down to under 13, at that point the car starts to die out. Doesn’t happen at the 1000 rpm idle. The bac has the correct ohms per fsm, but the bac screw is turned in all the way clockwise (lowers idle). It lowers the idle all the way to that point. I looked at the idle stop screw while the car was cold, and it wasn’t even touching the arm (thermowax?). Anyway I’m at a loss and need help.

 

Think I’ll get a new thermosensor (one for ecu) and see if that does anything

 

I'm also still interested in seeing your resolution on this as I still have similar issues with mine...

 

still haven’t figured it out, haven’t put in the thermo switch, did find a brake booster vac leak I’m going to try to fix though. Out of curiosity, which ecu are you running? I am using an Rtek 1.7, and From what I found with our issue, it could be Rtek related

 

Have you checked to make sure the throttle cable isn't over-tightened?

EDIT: Quick and easy way to do this; With the car all the way warmed up and idling, pull upward on the gas pedal. If there is no change, it's probably fine. If the idle dips, it's over-tightened.

 

There is a wee bit of slack, but I will do that test just to make sure.

 

Hey bud, have you checked that the primary throttle plate is returning to its home against the bump stop? There should be a dashpot (little round canister) on top of the throttle body. If the post on the bottom of it is stuck, it wont allow the throttle plates to return to their home against the bump stop. You can squish the post on the bottom of it in and let it return a few times to see if it still works.

 

my car has an Rtek 2.X with an old tune from the previous owner that I do not have the ability to view/access. My injector setup (also from the previous owner) is 720/750. I also recently bought a used rtek 1.8 which should be close enough to plug and play with my injector setup (secondary will be slightly rich but nothing crazy) just to see if that would help but I have not swapped it in yet, was going to try to keep messing with TPS, idle control on BAC, etc before I change the ecu.

 

mill check that, so just check and make sure the dashpot has free slowish movemnt