Have a 91n/a that is stock...the idle is fine when i have the headlights or under a slight electrical load... but when i turn the headlights off the idle likes to stay around 1000rpm if i keep pressing the brake it usually falls back to 750. Could my tps sensor do this??? It seems like the ECU is keeping the idle at 1000, i made sure that the fast idle cam seperates and the throttle plates close fully, the only other thing i can think of is tps sensor. Anyone know or have had this problem??

 

Your mechanical idle settings are too high.
Vac leak - too much air bleed (the screw in top of the TB) - hard idle stop still too high.

The TPS only tells the ECU to limit idle speed to >750 and < 1500.
The >750 idle is controlled by the BAC.
The <1500 idle is controlled by a fuel cut.

 

What he said. Jumper the "initial set coupler" (green, 2 pin connection, driver's side front corner) to turn off all ECU controlled idle settings, make sure the electrical load is as low as possible (lights & stereo off), and then tweak the idle with the screw on top of the throttle body (I assume that's where it is in the S5... if not, the FSM will tell you where it is).

Set the idle to 750 RPM or so mechanically, then remove the set jumper and the ECU should take care of it.

If you can't set it down to 750 RPM, it's possible that the hard idle stop is set too high, but since that is very rarely messed with, it's time to go hunting vacuum leaks.

-=Russ=-

 

thanks ill try setting the air screw on top of the throttle body

 

i don't know....dashpot have anything to do with it? just an idea. and don't rule out a vaccum leak.