Questionvehicle will crank up rev up then settle down and run bad. seems to get better as it warms up or if you unplug maf sensor. codes were p0300 p1166 p1167. replaced pre cat o2 sensor on both banks bc of tsb we saw. bank 2 pre o2 sensor shows no activity unless you punch the gas or add starting fluid while running or pinching fuel pressure reg. or unplugging maf sensor. we took front o2 sensors out to check cat's for plugging it still ran bad, replaced fuel pump assembly also. any other ideas
AnswerIt's difficult to determine whether you have one or two problems here.
P0300 indicates a random or multiple cylinder misfire.
P1166 and P1167 indicate that the ECM is unable to alter the amount of fuel enough to get the oxygen sensor readings to the desired values. Since you have both P1166 and P1167, you should be looking for conditions that are affecting both banks of the engine.
In this case, you're looking at three possible scenarios:
-- The misfire is causing the abnormal oxygen sensor readings
-- The abnormal oxygen sensor readings are causing misfires
-- There are two separate issues
I'd recommend to start with checking for the following:
-- vacuum leaks (manifold gasket, pcv hose, etc.)
-- improper fuel pressure (low or high)
-- stuck open purge control valve
-- faulty air flow sensor
-- leak in air intake bellows
