When you accelerate it probably does not quit blowing but rather
blows out the defroster vent. This would indicate a vacumn leak or
possibly a bad vacumn check valve. The check valve is located in
the vacumn line that goes through the firewall somewhere between
the firewall and where it connects to the engine. Check the vacumn
with a vacumn guage (pump) in line going into the dash for vacumn
leak. Hope this helps. Keith