98 GM rough idle at start 2 codes found

[thewishkah]

Ok when I bought the car the CEL was on , and when sitting over night in the cold would be rough when started but would run fine once warm. I also noticed that I am only averaging 10mpg with a light foot. I know these aren't fuel friendly cars but I should be getting more than that with mixed city/highway driving. I got the codes read and these are what they were...
P0171 and P0174 both having to do with fuel in some way. Are these common codes for these cars? Is it the MAf, or the O2 sensors? Id rather start cheap with parts replacement before I waste money that doesn't need to be spent on a fix. Any info would be great, Thanks Jon.

[1990LTD]

A quick jaunt to google tells me those are codes to tell you your car is running lean, generated by readings from your o2 sensors. One is from each bank of cylinders (you've got a sensor on each)

http://www.aa1car.com/library/ford_lean_codes.htm

Ford P0171 & P0174 Lean Codes
Copyright AA1Car

A Ford P0171 is a LEAN code for cylinder bank 1, and P0174 is a LEAN code for cylinder bank 2. These codes commonly occur on many Ford vehicles, and are set when the powertrain control module (PCM) sees the air/fuel mixture is running too lean (too much air, not enough fuel).

When the Check Engine Light comes on, either one of these codes, or both, may be found when a code reader or scan tool is plugged into the vehicle diagnostic connector. IF the vehicle is driven long enough, typically both codes will be set.

A P0171 lean code for bank 1 is the cylinder bank on the RIGHT (passenger) side of the engine on Ford vehicles with a V6 or V8 engine and rear-wheel drive.

A P0174 lean code for bank 2 is the cylinder bank on the LEFT (driver) side of the engine on Ford vehicles with a transverse-mounted V6 engine and front-wheel drive. This code is not set on four cylinder engines (no bank 2).

WHAT A LEAN CODE MEANS
A lean fuel condition may exist if the engine is sucking in too much air and/or the fuel system is not delivering enough fuel. If bad enough, a lean fuel condition may cause lean misfire, a rough idle, hesitation or stumble when accelerating, and/or poor engine performance.

Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow (because the EGR differential pressure sensor that monitors EGR flow is faulty and is under-reporting EGR flow).

If the problem is not enough fuel, the underling cause may be a weak fuel pump, restricted fuel filter, leaky fuel pressure regulator or dirty fuel injectors.

check for vacuum leaks

[thewishkah]

Thanks for the info, now could this be the main cause of the terrible gas mileage that I have been seeing? maybe it sees that its lean and is trying to send more fuel? or is that not a possibility?