I'm trying to dial in my S4 TII throttle body and need some clarification on fast idle cam adjustment. I have been operating under the assumption that the two marks on the fast idle cam are "engine not warmed up" and "engine warmed up"



But I think that's wrong. I found another thread with this image from the S5 na manual that mentions a 32degF mark on the fast idle cam:

Does that mean that the thermowax retracts at near freezing temps to open the throttle even further upon startup, and when I'm adjusting the fast idle cam on a warm day with the engine not warmed up I should aim to have the 77degF mark touching the roller, and the cam not touching the roller at all when the engine is hot and the thermowax pushes out?

 

The wax does retract more under colder temperatures. You will set the cam to the room temp mark (77f with your engine cold). If you're anywhere around that temp, it will be fine. Its not that precise of an adjustment. It will give a little more throttle when the engine is really cold. When the engine warms up, the wax pellet will swing the cam free so the throttle shaft won't even be touching it. Once you set it, completely warm up the car and ensure that the wax completely pushes the cam out of the way. If it doesn't, you will need to replace the wax pellet.

 

I stuck my throttle body in the freezer as an experiment, and I did indeed observe retraction of the thermowax rod. The 0/32deg mark on the fast idle cam didn't quite reach the center of the cam roller, but I don't know exactly what temperature everything is at (my infrared thermometer isn't working).

 

The critical thing is to make sure the cam clears the throttle while the engine and thereby the throttle body are hot. This is when you set your engine idle because it means that the throttle plates are at their minimum aperture as set by the throttle stop screw (which is NOT the idle adjustment screw). If you haven't touched the throttle stop screw, don't change it. This is the base point that your ecu uses. This is where your tps sensor is set. If you haven't messed with the stop screw, you just set your tps once and it's good for the life of the sensor. The idle adjust will come from idle adjust screw on bac

 

basically there are two adjustments. the fast idle screw adjusts how high the fast idle is, and the cam adjust screw is when the fast idle is, or at what temperature.
the factory setting is ~1800rpm give or take (if you measure at the throttle stop the throttle is open about 1mm/0.040")
and it should pop off about 65c

i like to lower the rpm a bit, they were trying to get the converters to warm up as fast as possible, and i'd rather save the fuel.
and then if you live someplace warm, like California you can have it pop off earlier.

ive also found that it can take a couple tries to get it where you want it, and the cars vary, so set it like the book, and then season to taste


65c is basically here on the gauge,

 

I did also confirm that my thermowax rod extends and now have the fast idle cam disengaged from the cam roller at full extension.

This is the throttle stop screw, right? Thankfully mine still has the factory goop and I haven't (and won't) mess with it:



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It’s more about duration of how long it stays in the warm up cycle. But as others said make sure the cam does disengage from the roller when warm. Also check the roller for flat spots and that it does move or you will have to reset the cam if the car is sat long enough. This is just a quick gas pedal stab before starting