2001 boxster runs very poorly after filling tank.
 

This is a consistant problem. When I fill the tank, even if I stop a little less than full, the engine starts to perform badly. Pops, won't take gas from idle, pushing down accelerator and nothing happens or takes along time to catch up- , huge hesitation 2nd gear around 2800 RPM, Then can feel it hesitating as I an traveling on flat road. After maybe 10 miles and shutting the engine down and starting the next morning, problem is gone. Dealer has installed air-oil separator and couplling, Mass air sensor, cleaned throttle body. When it is okay the next day, it runs great with absolutely no driveability issues until tank up again. Any ideas would be welcome.

What mileage? motor? trans? any CEL? What error codes?

2001 boxster runs very poorly after filing tank
 

Engine is 2.7L, 5 speed, 40K miles, no CEL and no pending codes. Iam thinking some crud in tank that gets stirred up when filling up, or fuel filter. Any other suggetions would really be appreciated

Sounds like it's got to be fuel system related. Next time you get about halfway through a tank, drop in some Techron... like a whole bottle. Maybe it's dirty injectors? Maybe something is messing with the pressure at the fuel pump (the one in your car, not the ones at the gas station).

Not much to go on with no codes. Clearly a fuel system problem. Possible causes:

Overfilling/topping off the tank
Bad gas cap (usually causes CEL)
Evap. system problem - bad vacuum tubing/clogged tubing, evap. cannister purge valve (usually causes CEL)
Fuel filter clogged

Anything I missed?

Is the car difficult to start after you fill it up? I had some of the same symptoms you described, but based on your report mine were a bit more severe. My car would be hard to start and then stall several times.

I had a CEL for the Mass Air Flow sensor. After replacing that I had another CEL for the evaporative system. That required the replacement of a hose and check valve in the evaporative system. Since then, I haven't had a problem.

The technician who repaired my car warned against overfilling the gas tank. Basically he recommended that I stop fueling as soon as the pump shut off automatically. Apparently topping off the tank wreaks havoc with the fuel system. I'm not sure I understand how that causes a problem, but I've followed that advice and haven't had a recurrence of my problem.