My brother's car kept going into paroxysms where the engine would stutter and want to die, at random times. He'd pump the gas etc and it would go away.
Never happened when he was at the shop, so the guy said "If it does it and you're anywhere around, drive right in and show me!"
Kind of a long shot but what could he do? So one day it happened around 5 and he was close so he pulled in.
They shop guy listened a moment, said "don't do anything!" and ran and got a vise-grips. He shimmied underneath the car, clamped the fuel line. Waited until it almost died, then released.
The problem disappeared! It purred like a kitten.
"It's almost 5, I want to go home, but bring it in Monday and I'll take care of it."
"You have to explain that!"
"A piece of grit got into your needle valve (fuel rate control). Starving the engine made the valve fully open, and the grit passed through. I'll replace your fuel line and filter, problem should go away."