Engine Performance problem
1994 Ford Taurus 6 cyl Front Wheel Drive Automatic 82,000 miles
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1994 taurus 3.0 with 82k miles. Getting a rough stumble on cruise and idle, and an occasional backfire under acceleration. fuel pressure is steady at about 35psi on idle, but when put into gear with the breaks on it fluctuates between 30 and 35. when disconnecting the vacuum line from the fuel pressure regulator it stays solid at 40psi. is this normal? other things i have replaced include MAF, EGR, ACT, plugs, plug wires, cap, rotor. only trouble code is 565-canister purge circuit failure. no check engine light comes on though. vacuum seems fine to the evap canister. could that also be a problem? thanks in advance

Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires

I have yet to test the MAP and the fuel pressure regulator. I'll do those next chance I get. I'll need to track down an injector pulser so i can test the individual injectors for pressure drop. thanks for the info =)