1999 f150 4x4 , p1506

O2 sensor po136,front and back sensor to be replace.

He needs to check the fuel flow as well as pressure , All so a blocked muffler can have this affect

This Code is about the RPM not matching the idle settings. A Vacuum leak is tricking the engine into making adjustments based on a lean O2 reading. Correspondingly the O2 sensors are demanding more fuel to eliminate the lean readings. Then the engine realizes the amount of air going by the MAF is not matching the IAC settings(Because the air leak is increasing rpm) and blames the IAC which is a Code P1506.

With the engine running, use an old spray bottle and fill it with water. Spray the seams, vacuum lines and solenoids until you notice a change in RPM. Lastly, spray the EGR pod if the diaphragm is torn it will leak vacuum.

Wherever you find the leak, fix it, then clear the computer and drive it.

P1506 - Idle Air Control (IAC) Overspeed Error This DTC is set when the PCM detects engine idle speed that is greater than the desired rpm.

• IAC circuit short to GND
• Damaged IAC valve

Disconnect IAC valve and look for little or no change in engine rpm as an indication of a stuck or damaged valve.
Ford Idle Air Control IAC valve test how to adjust minimum idle speed
Ford Idle Air Control Valve Diagnostics High Idle DTC P1506

i would start looking for vacuum leaks first,

Idle Air Control

P1506 - Idle Air Control (IAC) Overspeed Error This DTC is set when the PCM detects engine idle speed that is greater than the desired rpm.

• IAC circuit short to GND
• Damaged IAC valve

Disconnect IAC valve and look for little or no change in engine rpm as an indication of a stuck or damaged valve.

This code refers to the Idle Air Control Overspeed Error, I would clean the IAC, and if cleaning does not work I would replace it. It is located directly on top of the throttle valve on the intake manifold. Hope this helps, let me know.

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.

p1131 means that the bank #1 O2 sensor, the bank closest to the firewall, cylinders 1-3 is showing a lean mixture. Could be a vacuum leak, a misfire on that bank, an exaust leak upstream of the O2 sensor, fuel control or injector problem on that bank, a faulty O2 sensor, faulty PCM, faulty wiring in the engine control wiring harness.

P0171In the vast majority of cases, simply cleaning the MAF sensor does the trick. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling also Inspect all vacuum and PCV hoses, replace if necessaryCheck for a dirty fuel filter and proper fuel pressure

look for a diagram under the hood follow the route for each vacum . you have a intake leak take your time and go over each side of the engine even plastic air line could be cracked