89 FJ runs great...then not.

[laseron]

I've had some problems with my FJ running badly after good startup and running for several miles. Suddenly, and without warning (is there any other way?) it stumbles, and loses power. Applying throttle makes it worse, to the point of stalling. Thinking it was a fuel delivery problem, I replaced the fuel pump and filter. No change. There's no trash in the fuel tank, gas is pretty fresh. Now it looks like a carb rebuild would help, but that still doesn't give me hope. Maybe it's the computer (original still installed). Maybe it's Jupiter.

[FJmonkey]

If you have a spare key then try opening the tank when you have this problem. If the tank can't vent, the pump will vacuum lock. More common with earlier years as they don't have a fuel pump.