Getting in with a 2.9 is not totally unheard of, so wait and see. In the event that you are not admitted, you should do all that you and e.regina mentioned above. Also, have you looked at engineering graduate certificate programs? Some schools let you start with one of those and then roll it into a terminal masters degree. With a masters, and (presumably) a good GPA in a masters program, along with the ideas in previous posts, you could help yourself significantly towards a PhD admission.