hugues

I am talking about the temp. sensor on the dynamic chamber (not to be confused with the one in AFM). For S4 NA but should be relevant to others.

I wanted to see the effect of temperature of air entering the engine on the IDLE rpms.

So, I got engine fully warm and got the voltage at the intake temp sensor (2.90V). Outside temp is 60 degrees F. Idle is at 800 rpms. Sounds good.

Now, I drive along some long stretch and come to a stop. Voltage at intake temp sensor is now 3.20V, meaning intake air is colder than what it was before. Idle speed is 1,100 rpms.

I have made sure nothing else that matters for the BAC valve changed between the 2 measurements.

Assuming my car is working like it should, the ECU is boosting the idle a bit when the intake air temp goes below some value. Of course, it makes sense but I think that's too conservative (unless my sensor is out of range). I would think the cutoff point corresponds to 3.0 V on the sensor but I am not sure.

I kinda wish the cutoff was higher, that would save me some gas. If somebody has an intake air temp sensor lying around, I'd be glad to take it off your hands.

HAILERS:
in case you read this, can you check this diagram and confirm that it is incorrect (yellow and orange lines crossed)
http://www.geocities.com/huguesdc1/faqvacuum.html

hugues-

WAYNE88N/A

Your temp sender voltages match mine, which means either we're both good, or both bad, lol...

3.2v at cruise (70 mph, about 90*F out at the time)
2.4v heat sink (30 min. after shutdown)
3.7v cold start

You gotta figure, the intake air is in an expansion phase by the time it hits that sensor, because the air mass just made it past the throttle plate restrictions. Expanding air cools...

I'll give Hailers some more time to look at your diagram, then I'll chime in later

HAILERS

About the jpg: The GREEN line should be identified as the line that feeds air TO the fuel injector air bleeds. I'm pretty sure that is right. I'm talking about the middle of the three lines at the front of the dynamic chamber..

Yellow and Orange some other time. N/a is not available right now. I'm never been able to keep those two lines above the acv straight in my mind. I always have to idle the car and pull the blue plug off the Relief solenoid to find out if they are on the right place. If the air dumps overboard when I do that, then they are on right. If the air does not dump out the bottom of the acv...then I've got them crossed.

WAYNE88N/A

The two lines above the ACV, side-by-side:

Aft nipple is for the relief solenoid valve circuit (connects into the lower hard line coming off of the rat's nest at the back of the eng)

Fwd nipple is for the switching valve...

The FSM picture is kind of ***-backwards as far as those two vac lines go...

hugues

Thanks HAILERS and Wayne:

HAILERS once told me the tale of the 2 R's of emissions: Relief is Rear.

So, the diagram is wrong right (orange and yellow should be switched after the rats nest) ? or have I been staring at it too long ?

hugues-

hugues

ok, I have gone ahead and change the vacuum diagram on my page. It should now be correct. The yellow line now connects to the Rear nipple. the orange one to the front.

hugues-

WAYNE88N/A

It's not so much that your colors were wrong (it depends on how you look at the FSM diagram compared to the actual engine layout), but that the FSM picture shows the lines routing around the FRONT of the engine, when in fact they route around the rear. So you don't know whether to look at the diagram literally, or just for reference purposes...

Good job with the pic, though, I've become rather obsessed with my vac routing lately fighting this "mini-hesitation" thing I've got going on, and when I pull the UIM off this weekend, I'm going to color code all of the seperate systems, and paint the metal lines to match (blue for relief, orange for PRCV, grey (silver) for switching, red for purge valve lines, and yellow for all vac sources (EGR is long gone). Gonna have a rainbow nest, lol...