'99 Boxster Decelerates, Loses Power

[keithl]

1999 with 63,000 miles. Car started to decelerate, acted like it was having trouble getting gas, would intermittently surge forward then decelerate. I pulled over shut the car off, restarted
and the car drove fine. No check engine lights.

I replaced the fuel filter. Today, same problem. Car starts to decelerate, I give it gas
but the engine is having trouble revving. I stop and restart, the car runs better and I am able to return home, but doesn't run 100% smoothly. Again, no check engine lights.

Does a fuel pump go bad intermittently? I don't think it's bad gas. Ideas?

Oil cap is not hard to remove when car is running. Engine runs rough with oil cap off and smooths out when replaced.

Thanks.

Anyone, Anyone, Bueller....?