I've post before about an idle problem I have been having, and have done much searching. Please if anyone can help me with this one it would be great. I found one thing out today I believe.

I recently replaced my AFM in hopes that that may help it, and I am not sure if it did or not, but one thing I notice now which I am not sure was true before is if I do not have my heater fan on the car will idle at 1500 at will pulsate. You can try using the throttle to get it to go down, but usually this doesn't work. When you turn the heater up to high the pulsating stops, and what is even more interesting is the idle will usually now go down to 700 rpm while driving, but once you turn the heater fan off it will resume going to 1500 and pulsate.

I am not sure if I had it on cool air if the same thing would happen or not, but perhaps it would. Also I don't know if the fan must be on high. I can do more experiments if it would help people eliminate possibilities. I am going to change the tps next, and was thinking of a BAC cleaning.

The main question I am looking an answer for is why would turning the heater fan on effect the idle. How does the system working differently with it on vs off? I don't understand the car well enough to know what actually is affected by using the heater (or perhaps just the fan again don't know if it has to be hot air). Thanks in advance!

 

pulsating is from a TPS being out of alignment. Adjust the TPS back into spec and the pulsation wil go away.

The A/C switches on the BAC, in addition electrical load on the S5 models activates the BAC.

BAC increases idle.