1999 windstar lx rough idle

[nelzone17]

My van has recently started to idle rough to the point it dies.It dosen't do it all the time, mostly after it has ran a while. I noticed something odd when it was running bad the other day. The needle on the fuel gauge was moving up and down. I know this can't be normal. The cel is on, in fact it has been on. I get codes 171 174.Any help would be appreciated

[wiswind]

The codes that you list are an indication of a lean conditon on both banks of cylinders.
Have you done the isolator bolt TSB?
The top sticky post provides a lot of information about it.
That is the FIRST thing that I would think of to advise.

If you already have the improved isolator bolts, the most likely cause is still a vaccum leak.
Those can be difficult to track down.
Also, are all the routine tune-up items up to date?.....spark plugs, spark plug wires, fuel filter, air filter, etc