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You could have a bad mass air flow sensor. This is a very important sensor input to the computer. It uses a hot wire sensing element to measure the amount of air entering the engine. The MAF sensor then outputs an analog voltage signal to the PCM proportional to the intake air mass. The PCM calculates the required fuel injector pulse width in order to provide the desired air/fuel ratio. If the sensor is bad than this air/fuel ratio will be off causing severe performance issues. In extreme cases, I have seen these two problems cause a no start condition. This can be bad both ways over or under estimating air flow into the engine which can result in a lean or rich condition.
I would rather have you check if first.
If you need help, let me know.
I would also like you to check fuel pressure. If the return line is kinked or there is some obstruction, fuel pressure could be way to high and cause your rich condition.
First start by checking the voltage with a volt meter.
Mass Air Flow Sensor
Key-On-Engine-Off 0.0-0.2 V
Idle 0.6-0.9 V
You will have to clear the computer by disconnecting the battery for 2 minutes.
Also, sounds weird, but, when you get it all back together. do a few Wide open throttle runs from 0 to 60. THis is how the ford engineers update the Baro pressure in the computer. WIDE OPEN THROTLE. Because the mass air flow sesnor is i control of the baro pressure you will have to run this procedure after you get the new mass air flow sensor in.