Duratec Lack of Power

98' Sable w/duratec, 92,000 "pampered" miles. All maint., filters, etc. performed as recommended. Use injector cleaner at every oil change (3,000). Car had major tune-up, new plug wires, throttle body cleaned at 88,000. Ever since, have noticed lack of power when taking off from a dead stop (red lights, etc.) usually with AC on. Once car gets started it will accelerate rapidly. It's as if it boggs down and then takes off. No problem with idle or normal driving. Just happens with moderate acceleration from a stand still. Otherwise, engine performs great and has lot's of punch at high speeds. Also, gas mileage is DOWN about 3 mpg. since tune-up. Anyone have any ideas?

Fuel pump?

i have a 99 also after i made my custom intake my car seemed slower at the line. I changed the fuel filter and picked up better. But I found now if I ease into it its much faster.

There is a small bell crank connector that opens and closes the secondary intake ports (according to engine RPM) and is connected to the primary throttle valve. When at idle or low engine speed the secondary intake ports are closed which keeps intake velocity high and provides good low end response and acceleration. At higher engine speed the bell crank opens the secondary intake runners which provides for good high speed performance. The metal rod on the bell crank often pops out and if the secondary intake port runners are open at low engine speed the engine has poor throttle response and low end power. The fix (providing the metal connecting rod hasn't fallen off the engine)is to replace two small plastic snap in connectors that attach the conecting rod to the main throttle and secondary intake port control. They are $7-8 each at Ford dealerships. I have corrected this exact same problem in many 24V DuraTec engines. Hope this helps.

I have a 96 with the duratec engine and experience the same trouble about once a year. The dealer replaces the "Power Valve" and it runs fine for another year.