I have a 94 Jetta that must be possed! Hot days seem to cause the problem more than cool days. It idles rough. It loses acceleration or hesitates at stop lights so that you think it is going to stop & you’re going to get rear ended.
I have had it at the VW dealership three times this year & they haven’t found the cure.
They have put new plug wires, plugs, flushed the fuel injection, even put in a new distributer$$$$!
I am now thinking that perhaps it could be something like the charcoal canister? Any ideas?
Looks like your shop is on a fishing expedition at your expense. I would like to recommend you look for another tech, preferably an independent. Shop around.
In the meantime:
Fuel pressure constant?
When was the fuel filter last changed?
Air filter clean.
Check for vacuum leaks (hoses, intake manifold, etc).
Check the IAC valve (if equipped). (Idle Air Control)
You mentioned the charcoal canister. Any specific reason?
Do you regularly ‘top off’ the fuel everytime you gas up?