well i have had my car sc'ed for a month now.
quick recap:
-V1
-3" intake piping
-tial BOV
-3.6 pulley
-BEGI adjustable FMU
-cattman y-pipe + greddy evo2
-stock injectors.

the idle problem is that when the AC/Heater fan is turned off, it will idle low, them jump back up to normal, then idle low again...., after awhile it will throw a P0100 code and then i cant rev past 2500rpm

however, if i have the AC/Heater fan turned on, then it will idle fine, just staying at a constant position.

there are three vacuum lines that are not plugged into my intake piping, and from the questions i asked on here, i received a response that it was trivial to have them plugged into the intake piping; 1)air temp sensor, 2)vias, 3)and this other vacuum line that runs across the front of the intake manifold, connects into some part near the firewall that has another vacuum line running out of it that connects to the intake manifold immediately after the throttle body.

also, i had thought that it was my MAF dying, so i bought a new one and installed it, and the exact same problem happens.

any thoughts on why it would idle well when the AC/Heater fan is on but not idle well when it isnt on?

 

What's your idle at? Turning on the AC kicks up the idle, that's what's smoothing you out. Are those vac lines just laying open? IAT shouldn't have a vac line (but I don't know 5th gens that well), probably the boost sensor you're looking at.

Pics of the last unconnected vac item?

 

my idle will jump from around 500-900 with the AC/heater fan off, but when turned on, it will idle at 900rpm

here is a pic showing that i have the 2)vias and 3)the other vacuum line plugged in to get filtered air from the crankcase breather filter.


i gotta run to work, but i can get more pics later this morning

 

photobucket seems to be down, but here are pics on flickr

http://www.flickr.com/photos/8727357@N06/

 

i spent about an hour and a half working on my intake piping today, and i got the car to run now without stalling when the AC/heater fan is turned off.

all i ended up doing was changing where i have the BOV at. it is now immediately after the elbow that comes off the blower.

i also put my original MAF back on, and that help to smooth out the idle ALOT. i know that the newer MAFs are supposed to be a little different in how they meter air, but i think that is what made my idle horrible.