1999 Cadillac Deville P0171 and P0303 Engine codes, Engine

KLIXIE3

MEMBER
1999 CADILLAC DEVILLE

Engine Performance problem
1999 Cadillac Deville V8 Two Wheel Drive 118000 miles

It started with a P0307, so I changed all plugs and wires, code went off, then came back on a day later. Replaced the coil pack linked to that cylinder, then the code went to a P0305. Changed the other three coil packs, light went off for a few days. Then the light changed to a P0303 and has been on for a month. With A/c on idles rougher, but still idles a little rough without A/c on. Gas mileage has been very poor. Is this a MAF, or could it be an Oxygen Sensor?

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

P0171

A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (Try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)

Check cyl no.3 sparkplug/compression/injector-