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Ford Escort DTC P0171 And P1506

Q. I have a 1999 Ford Escort 2.0 liter SOHC, automatic transmission and 77,000 miles. It runs fine but sometimes, about one time out of eight, when I start it I get a BIG cloud of blue smoke. I have replaced the valve seals but it seems to have had no effect. The service engine light also came on with trouble codes P1506 and P0171.

Ford Escort DTC P0171 And P1506

Are these all part of the same problem or are they separate problems? Otherwise the car starts and runs well.

A. DTC P0171 - System Lean and DTC 1506 - Idle Air Control (IAC) Overspeed Error.

DTC P0171 indicates a mixture leaner than the HO2S can correct for.

DTC P1506 is set when the PCM detects the engine idle speed is greater than the desired rpm. This is most commonly caused by a dirty or bad IAC valve. Cleaning the throttle body will, most likely, cure this problem.

The P0171 is probably due to a dirty Mass Airflow Meter. This has been discussed here many times.

Ford F150 Codes P0171 & P0174

Ford Expedition P0171 & P0174

Ford Mass Air Flow Sensors

As for the cloud of smoke, it may be due to a blocked PCV system or the valve seals were not installed properly. The oil could be coming up through the rings. A wet/dry compression test will tell that.

Additional Information provided courtesy of ALLDATA

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