Idles extremely high when shifting gears and when slowing down or coming to a stop. Putting it back in gear and letting off the clutch is the only thing that lowers rpm's. It will go back to normal if you kill the engine and restart it but the problem continues once driving again. Throwing codes p0171 and p1506. Any ideas on diagnosing this issue?

 

Welcome to the forum

P1506 Idle Air Control Overspeed Error

Fuel injected engines can't use an "idle screw" like a carburetor did, they use a Air Valve that bypasses the throttle plate to let more or less air into the running engine to set idle on the fly, Ford calls theirs the IAC(idle air control) Valve

This P1506 code means the computer has closed the IAC Valve all the way but the idle remained too high(overspeed) so computer can't control idle
This usually indicates that the is an "air leak"(vacuum leak) somewhere in the intake manifold
Could be a cracked vacuum hose or unplugged hose, or a gasket leak(less likely)

P0171 System too Lean (Bank 1)
A 4 cylinder only has one bank, Bank 1, a V6 or V8 has two banks

This code fits with the above code in that it also indicates an air leak
The computer calculates how much fuel to add to the running engine based in engine size(2.5 liters) and air weight and temp
If unreported air is coming in from a leak then computer calculations would be wrong, computer would add less fuel than needed, so "lean" would be the code
The engine is NOT RUNNING LEAN at any time, thats not what the code means, it means the computers calculation was "lean" so its reporting that to the driver
The computer adds more fuel as needed


So both these codes point to an air leak in the engine system, usually intake manifold
Also check PCV Valve and hose
PCV valve should be replaced every 3 oil changes, they can stick open causing your symptoms and codes

 

Thank you. You're answer was very clear and easy to understand. Is there a possibility that because the battery has been disconnected on several occasions recently that I might need to perform some sort of a reset to the system? And if so, how is that done? I thought that might be a good place to start before I start trying to track down other possible causes.

 

Disconnecting the battery(for longer than 5min) is the reset for all modules in the vehicle, so that's been done
Doesn't hurt anything
Wouldn't cause high idle

Engine should idle high when started Cold, then idle should slowly come down over the next 5 to 8mins of run time as engine warms up
So you do have air leaking in from somewhere between the throttle plate and the cylinders, which is the throttle body and intake manifold areas