Would a blown brake line affect the start of a 1992 Mazda truck?

Brake lines are in no way connected to the engine. Brakes are a hydraulic system and is separate from the engine. "IF" you are talking about a vacuum line, you may have trouble starting or runnning the engine. There is a vacuum booster behind the brake master cylinder. The vacuum or suction from the engine pulls on a rubber diaphragm to assist with braking, If the line or hose is broken, you will have some trouble with the idle. It would normally increase in this situation as the engine is getting more air through the hose instead of through the air filter.