I have always left it overnight so they can see what it does. The place I left it Monday night said fuel pressure dropped below where it should be (can't remember what he said the pressure was but is dropped a lot). That is why he thinks it is the fuel pump or possible the fuel pressure regulator. I told him to change that first and see what it does after. I have not heard from him yet today. Last winter is the first time Service Engine Soon light ever came on and the codes were 171 and 507. As I said before this started in Nov 2010, nothing changed after mechanic
replace MAF and one other sensor (can't remember which one). Next Nov (2011) they changed the fuel filter when I had it serviced and it went all winter with no problems. Late 2012 would do it once in awhile and in 2013 was worse. Has started off this winter bad. It has 127,000 miles on it has been overall a good pickup. UPDATE Just heard from the mechanic
and he did find a leak in the intake gasket. Hopefully this will fix it.