01 Prizm P0171

"" wrote: > 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? > > Al

If im not mistaken that code is: system to lean meaning O2 sensor. Replace the o2 sensor.

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 replacement.

Steve

Steve,

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.

Al

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.

Al