Your auto repair questions answered about a 1998 Ford F-250 With a MAF Problem.
This weekly Q&A session answers your questions about cars and trucks. This week explores a 1998 Ford F-250 with DTC's P0171 and P0174.
Question: 1998 Ford F-250 Mass Airflow Sensor
I have a 1998 Ford F-250 I just got done reading a response you wrote to someone else about a similar problem, so I was hoping you could help. It started about two months ago. My truck was running fine and my Check Engine Light came on. So I took it to AutoZone to use their OBD scanner. My truck pulled codes P0171 and P0174 so they recommended just cleaning my Mass Airflow Sensor. So I cleared the codes went home and cleaned it with Mass Airflow Cleaner.
Did normal driving and the Check Engine Light came back on I continued to use the vehicle for a couple of weeks because it ran fine. And the light did shut itself off About a week later it came back on except when it did now all of a sudden I had a terrible idle problem and it will shut off at times. Sometimes it idles super rough and others it'll hold the idle at about 1,500 to 1,200 rpm's.
I've changed the fuel filter and cleaned the Mass Airflow Sensor and still get the same code. Other than idle it runs good, because this is my only way to get to work I have to deal with it until I can figure this out, and upon warm up it runs great. It's got a 5.4-liter V-8. What can be causing this?
Answer:
The two P0171 and P0174 codes are quite often related to the Mass Airflow Sensor (MAF), which are prone to getting dirty. Another possibility for those codes is the Coolant Temperature Sensor (CTS). Quite often the CTS goes out of range and tells the computer the wrong engine temperature. It could be telling the Powertrain Control Module (PCM) that the engine is hotter or colder than it actually is. In that case the PCM will either lean out or richen the fuel mixture based on what the CTS is telling it.
If it is telling the PCM the engine is hotter than it actually is, the PCM will lean out the fuel mixture causing an excessively lean condition and cause those two codes to set. What you need to do is let the engine sit overnight so it is completely cold. Then connect a scan tool and see what the CTS is reading. It should be within three or four degrees of the ambient air temperature.
Another possibility is the brand of air filter you use. Some air filters are impregnated with oil to help them filter the air better. But this oil will flow in with the incoming air and get deposited on the hot wire inside the MAF. Cleaning will remove the oil but it will build up again in a couple of weeks. The best thing to do is get an air filter from your Ford Dealer or get a Motorcraft air filter from a parts store that carries them. Also, when you clean the MAF, a Tuner Cleaner from Radio Shack is recommended. It is much better than the automotive MAF cleaners.
That's all for this week. Feel free to browse the archives for past topics and other resources. And, as always, if you are stuck and need an immediate answer you can always call Vince on the phone.
