Weird XR4Ti behavior (no Audi content)

[JOSEV@samson-transport.com (Jose Vicente)]

Hello guys,

This is not an Audi issue, and I appologize for that, but I am a 
sworn Quattro fan and I hope someone here can help me. 

I tried putting a dump(or blow off) valve on my '85 XR4Ti and as soon 
as connect vacum to it, the car does not hold idle.  I understand that 
because of vacum at idle, the valve opens and draws in air wich is 
not meassured by the airflow meter and that's why I have no idle,
I can live with that, and at least I know what's happening.
Here is where it get's weird, I had the same exact set up on my '88 
XR4Ti, I had the same dump valve, same Intercooler and piping and I 
was getting vacum from the same place, yet I never had any idling 
problems and the valve worked beatifully. I looked all over the place 
trying to find a vacum or intake leak or something else that could be causing 
the car to stall, but I found nothing. The only thing I found was a 
small vacum line that was pluged. This line comes out from the T wich 
splits the power brake assist. I don't have my "88 to compare it to 
but on my '86 parts car the line connects to a small metal tube wich 
runs behind the engine and under the passenger side floor. I dont 
know where it ends. My parts car is an an automatic (I know that's 
sad but for $200 I can't complain) so I'm wondering if that line 
it's there because it's an automatic or am I missing this line on my 
5 spd. The only other thing I can think of is that the computers are 
different from the '85's to the '88's, but the set up is exactly the 
same, there is no extra sensors, sending units etc. I know Rapido and 
some of the other guys sell a dump valve with their intercooler kits, 
do you know how they route it?. Do you know what the best place to 
get vacum from is?. At first I thought the diaphragm on the valve was 
bad so I changed it but I get the same results.

Any help would be greatly appreciated.

Thank you 
RALLY ON
Jose M. Vicente
'85,'86,'88 Sierra XR4ti's
'87 5KTQ