2001 Ford focus when accelerates speed drops
and cut off restarts but no check engine light had
replaced fuel pump mass air sensor what's wrong
Sounds like your egr.
What is that
Its a sensor, that controls fuel pressure ,
Hopefully they changed the filter when they changed the pump and pickup up screens. EGR does not effect fuel delivery and would only effect idle speed by being stuck open.(it feed crank case gases into intake air to be burned during drive speed) It needs to be but on an OBDii tester and look at live parameters of fuel pressure, throttle position, mass air flow etc values to make and informed action. Live data also helps with diagnostics to see if key systems are working. You just don't replace things with out testing. TOAD (for the DIY) is an inexpensive software package that can look at those parameters letting you know if they are working.
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