Trouble with S80
 

Have two Volvo S80, - one Volvo S80 2004 2.4T

This morning filled it with 91 vs 87 Gas and after 30 min got check engine light. Is this is likely caused by change of gas ? or this is just coincidence ?

Second Volvo also S80 2003 2.9 - around month ago, I realized that I don't feel air blowing inside. I.e. I can feel that air condition working ( can feel cold air and I can hear noise on high settings ) but no air coming out of holes. :) What can it be ? Also approximately after 30 min of driving I can hear hissing sound coming out of break pedal and I have to push it up in order for his sound to stop. Can it be vacuum booster ?

second volvo probly has a shot blower motor, first volvo will blow up within 3 days

just kidding, go get it scanned for free at one of those auto zone shops ( i think ) sorry im in canada, here its part source that does it free

and you should have been running 91 from day 1 in your '04

As andrei3333 mentioned, you shouldn't be running 87 in a turbo'd Volvo.

even in a 2.9 its a high compression engine im pretty sure my manual says 91 for both