brake booster?????????????????

91 1.9l dies when brakes are applied starts and runs fine untill you try to stop. is this the booster??? how can i test this??

There is a check valve in the vacuum line. You can test it by taking it off and blowing towards the engine. It should only allow air towards the engine. If it flows both ways or neither way, replace the hose and check valve. If this is OK then I'm pretty sure the diaphram in your booster is ruptured and you will need to replace it.