I have a 98 F-150, 4X4, 4.6L. A couple days ago when my wife started it, it idled real rough and the engine pinged and smelled of gas. After she punched it, it seemed to be OK. Today it seemed hard for the engiine to turn over. It finally barely started and I could hear poppng noise as the vehicle shook and had the fumes of gas. I tried to give it gas but it did not respond other than barely staying running. There is no check engine light on. I changed out the alternator a coulple of weeks ago but the battery seems to be charging. This is a secondary vehicle for my wife and she says this has done it several times recently but that it has always gone away after she starts driving it. Today it will barely idle and acts like it is flooded and the timing is off. Also, it has never seemed to have a hard time turning over before. Thanks for any help. Lee

 

IAC valve is dirty and hanging.

 

My reasoned opinion based on your discription is if you are smelling gas and the motor won't rpm up, the plugs are fouled from excessive gas until they clear out.
Look at the possibilty of leaking injectors or a fuel regulator with a leaking diaphram allowing gas to be forced into the inake manifold through the vacuum hose that controls pressure regulation at idle.
Also take a smell of the oil to see if you smell gas in the crank case.
Good luck.

 

Dead coil will effect the Rpm and rough idle and may dirty spark or dead spark plug.

past experience in my truck although its a 5.4 not the 4.6

 

I drove it around the block hoping to get a code. The engine had a hard time to keep running. The engine was pinging and sounded like a diesel if that is any help.

 

Another possibility is the EGR is being held open.
This will advance the ignition timing and allow exhaust gas into the intake and cause very rough running "when it's not supposed to".