i have a s4 tii and it won't hold idle when it first starts up. i have to rev it to keep it from dying, but when it's warmed up it will stay at idle no problem. is it something to do with the sub zero starting? can't figure out what it is. Anyone have idea's how to fix it?

 

Sub zero isn't it. There is a brass(sliver?) tube on the firewall side of the throttle body. It has a little "button" that pushes on part of the throttle body when the engine coolent is cold. This holds the throttle plates in the correct position for cold startup. My guess is that if you check this part when the car is cool, that it isn't holding the throttle open much or at all.

 

If the thermo pellet is bad, he wouldn't be seeing a change in idle when the car warms up. He'd just have the BAC and bypass solenoid send additional air for 17 seconds, then the car would drop down to normal idle (~750 rpm).

I would test the TPS to see if it is giving correct resistance readings at various throttle positions. It may just be that it's sending the wrong signals to the ECU when the throttle is opened up for fast idle.

 

Go here and download section 4b (this is the Factory manual) page 63/126 will show you how this system works. Good luck and be careful

 

I think you mite be right. the guy that i bought the car from said that the throttle body plates weren't closing all the way fast enough, so i think he messed with that button that slows it down or stops it. is there away to adjust it or do i need a new throttle body?

 

I have the same thing, S4 TII, same situation, have to keep it revved for a minute before it will idle. My thermowax (the button they are talking about) was bad and holding the throttle open even after warm-up, so I disabled it. Mine also has low compression, I think about 60-70 psi, and has to be started a certain way or it floods. I would check the compression on yours, as well as the t-wax, which can be replaced w/o buying a complete TB.

 

i checked the compression of the car and i was 110, so the compression is good. i'm going to check that thermowax thing. thanks!