This is in actuality a Toyota Corolla, but, many things can cause this code
in any car, low fuel pressure, clogged fuel filter, contaminated maf, any
leak in the air intake behind the maf ducting ,any vacuum leak, so this
means lots of diagnosis by someone familar with the condition. You could try
posting on a Toyota forum, there may be some common problem here.
> 01 Prizm. Sluggish off idle when cold. Feels like it's very
> lean and sets
> check engine light. Code is P0171. Any idea where to start?
> Any common
> problem to check first?
If im not mistaken that code is: system to lean meaning O2 sensor.
Replace the o2 sensor.
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Sheps right, it could be any number of vacuum or exhaust leaks. Could be
faulty MAF, coolant temp sensor or throttle position sensor. Could be
clogged fuel filter, faulty fuel injector or contaminated fuel. Could also
be a contaminated HO2S or faulty wiring.
It doesn't automatically mean your oxygen sensor is faulty and requires
After thinking about this, the coolant sensor makes the most sense. If it's
telling the ECM the engine is hot when it's really cold, it would be lean.
When the engine warms up it runs fine. The way I see it, when the O2 sensor
is cold it tells the ECM nothing so it must be running on some preset
conditions, altered by the coolant temp, throttle position and airflow. The
airflow would be the same hot or cold, and a leak would not change with
temperature, so the missing variable could be the coolant sensor. Unless the
throttle position sensor is not working at lower temperature?? I screwed
with it tonight, started it cold, but it was over 100 ambient:) Ran like
poop. If I hold the car with the brake, I can stand on it and it will not
pull at all. As soon as it warms up a just a little it will. I'm guessing as
soon as the O2 sensor gets hot enough to start feeding info to the ECM it
adjusts the mixture. BTW: The check engine lamp comes on, but will turn off
if you drive it a while.
Thanks for the help. Tomorrow I'll check the resistance of the temp sensor
hot and cold and see what I get.
This car is not mine so I don't know its history.Looked at it today. Was
trying to ID the temperature sensor when I noticed an oily film on the top
of the intake duct. Looked at it and saw the MAF sensor and connector were
oily. Removed the sensor, and the inside was full of oil. So I stuck my
finger into the intake track and no oil. Some damned fool oiled the MAF
sensor. Probably thought it was the throttle position sensor??? So I cleaned
it up and put it back in. We'll see what happens tomorrow morning.
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