running on impulse engines
In the original Star Trek series, whenever the main engines (warp drive) broke down (which was pretty frequent) the Enterprise would only be able to move using "impulse engines" - a low power, sub-lightspeed manouvering system based on a small fusion ram/ion drive.

By inference, someone described as "running on impilse engines" or "impulse power only" is either:

1. Very tired (a.k.a. 'running on empty')

2. Genuinely ill

3. (derog.) Slow and/or stupid.
"Jesus, I've just had to brief the sales guys on the new product.... they're all running on impulse engies up there".

"You want to go for a beer ?"

"No, man, I'm running on impulse engines... got to go home and grab some sleep."
