Help.... Confused and Engine Running Crappy!!!

Hey, I just bought a contour in september.... 1995 with the 2.0L 4 banger in it. For a few weeks now, the engine has been missing at low-mid throttle. I know by changing my wet spark plugs that its running rich. I have also changed my fuel filter, cleaned my throttle body, changed my AFM and an now throughly drivin crazy by this complex puzzle of an engine that lies taunting me from beneath the hood. Oh yeah... when its running rough, its making this wierd sound that almost sounds like a grinding hissing or something from somewher directly below the throttle body.... can anyone help me... I'm gonna go mad... Thanks

oh by the way.... though by replacing it i know its not the problem.... if I unplug my AFM, the engine runs great... figure that one out... Grrrrrrrr

Have You Changed Out Yor Egr Valve If Not Try That. The Othe Thing I Have Found That Causes This Problem Is An Air Mass Sensor That Is Not Properly Calibrated For Your Ecu. If You Did Not Give The Dealership The Calibration Codes Off Of Your Maf Sensor And They Gave You One Off Of The Shelf That Is The Root Of Your Prob,. If You Did Do That Then You Could Have A Bad Iat Sensor (air Intake Temp Sensor) Or A Vaccume Leake.