1. dive the bar down, way down.
2. Pick the D string
3. Raise bar at the rate you want to accelerate.
4. quickly dive bar.
5. Pick the A string
6. Repeat step 3 & 4
7. Pick the low E string.
This is what Mick Mars did on "Kickstart My Heart", and even though he is not near the top of my favorites players list, it does sound like a motorcycle.
My band opened a show for Vince Neil, so I witnessed this first hand.