According to Triple A, a rag stuffed in the tailpipe is a common way to check for leaks in your exhaust. If you stick the rag in and plug it in tight and start your car and the engine doesn't stall out, then you know there is a leak somewhere that is letting air escape. If there is no leak the car should die almost immediately.
Maura had an opportunity to get gas right before she turned into the White Mountain National forest and then about a mile before her wreck. There would be no other opportunities for her to even stop anywhere else. Once she turned into the forest, it's all trees and streams and country roads. It is a good four miles at least that she had to have driven just in the pitch black forest before she came up to the site of her accident. after her wreck she was stranded with her car for several minutes before the bus driver even approached the scene. the window of opportunity for someone who had sabatoged Maura's car ahead of time would've already came and went before the bus driver even showed up on the scene.
