You pulled your cord too far out, when you drove it it came out by itself, I've had that problem, try to get a new one and finish your break in/tuning. The HPI Rotostart will work, the HPI backplate won't, is too small. Don't put any rotostart in your car until you have a whole gallon trhough it, it voids the warranty. Your engine was stuttering and acting weird because it is still new, keep driving it around and start tuning it on the fifth tank (follow the instructions that came with it). It'll take you a while to tune it and get it right, once you do it, you're going to love your matrix. Good luck let us know how it goes.