Codes 171 and 455 on '04 GM 3.8

[Russ300H]

Hi All, need some help. My '04 Buick LeSabre started idling very rough after running only a few minutes. Once it is running at operating temperature, it seems to run fine. Average fuel mileage is down a couple of MPG from 18 to 16 city. Having the code(s) read two numbers came up: P0171 and P0455, Apparently some kind of leak in the fuel system somewhere, but nothing is obvious. The thing that throws me is that once it is at operating temperature is "seems" to run fine. Not that I understand all that much anyway. Any insight as to where to start is greatly appreciated

 

[MrMoody]

P0171 is usually a vacuum leak somewhere, or also can happen from low fuel pressure or filling a non-flex car with E85. P0455 is usually the gas cap. An evap purge line loose or leaking could conceivably cause both. If it happened suddenly, maybe something got knocked off or damaged. Carefully check all hoses. Vacuum leaks can be tough to find.

 

[Lubener]

Try cleaning the MAF for the P0171 and leaky gas cap or a leak anywhere in the evap system for the P0455. The steel lines in that system could be rotted out too.

 

[WyrTwister]

Do you have any way to test the coolant sensor ? Just guessing because you said it runs OK when it warms up to normal temperature . At that point what does the dash temperature gauge read ? Or does it have an idiot lite .

https://www.google.com/search?clien.....0....1..gws-wiz.......0i71.KduFICvk5X0

https://www.google.com/search?clien...HevhBlMQBQgrKAA&biw=1344&bih=677