OK. Right by the brake booster you will see vac lines going through the firewall.
Yellow is door locks.
Yellow/gray is vac. cannister in trunk
Green is climate control stuff
Brown is shutoff to key switch
Black is a vent line to under dash area

Golf tees or similar is useful here.
Unplug green line and put tee in rubber connector to block it. Start car, let run for 30 seconds and try and turn off.
Next, if it still runs, unplug yellow line, plug up connector and do the same.
These are the two most common.
The above assumes you do not yet have a Mityvac, which you should be purchasing shortly {around $30-35 bucks}
Also, this assumes you followed the large vac tube from vac pump at front of engine to make sure there was not broken tab off of it, or any unplugged vac line.
Since you didn't mention you had very hard brakes we'll assume the vac pump is working. And it isn't usually the shutoff valve.

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John