1986 f 150 won't start unless I floor gas pedal on 1990 Ford F-150

First I need to change year of F 150 to 1986. My truck used to start religously by just turning the ignition on. Now I have to floor the gas pedal and hold it to the floor or it won't start! When it does start it starts very rough and if I don't start it first try it floods and won't start unless I let it sit for a long period of time. What do you think needs attention??
Thank you for your time,
Roberto

Asked by for the 1990 Ford F-150
Has your gas mileage also decrease since this problem occurred? Pressing the throttle down fully allows more air to pass the throttle butterfly. So I suspect the truck is running very rich. Do you notice a cloud of black colored smoke from the exhaust?
I suspect a fuel injector has failed and is leaking, or a coolant temperature switch is reporting to the computer the ambient temperature is freezing outside and the truck needs a richer mixture (like using a choke to start an engine on older cars in the winter). Please let us know what you find out.
I have a 93 F150 with 5.0 it wont start unless u hold pedal to floor ,also has fast idle when it starts then slows down after few seconds
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