Didn't have a code just said the engine was running lean rough idle dies exhaust is chalky looking

Link below will tell you the code is a result of the rough running. Use the checklist to find the cause of the rough running and the idle speed should return to normal and the code should disappear.

https://www.obd-codes.com/p0506

check out these img for reference,replace the oxygen sensor and check for exhaust leaks.

You have to correct the cylinder misfires first

You may have vacuum leaks somewhere in the
intake or exhaust

You really need to look at data with a scan tool

You start with Mode $06 & cylinder misfire count ,if that
even works well on your motor

Then you look at fuel trim & add short & long together,
to get an idea if it is running rich,which would be a lean
condition from a vacuum leak or rich from leaking injectors

All the data is only good if you haven't cleared it or disconnected
the battery. If you did, then you have to drive until all I/M Monitors
run & then look at data

You look at O2 sensor data & even scope them

You made no mention of checking for codes
No mention of a cylinder leak down test for valve leaks
Exhaust Converter age or condition !
Fuel Pressure !

egr valve is stuck open at idel exhaust gas is entering engin causing lean condition and missfire your po300 301 codes replace egr and clear codes

It can be issue with low fuel pressure,the fuel pump is getting old both needs to be checked.Also get the IAC valve checked.
Go through the related help links with similar problem,it may help:---
Click the links below:---
Engine Idles Rough and Dies? http://whatisbyme.blogspot.in/2012/05/1994-lexus-es300-engine-idles-rough-and.html

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van idles rough? http://howtobyme.blogspot.in/2012/01/2004-ford-freestar-van-idles-rough.html

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runs lean and idles rough? http://technoanswers.blogspot.in/2012/02/ford-runs-lean-and-idles-rough.html

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Car still runs Rough after tune up?

http://howtobyme.blogspot.com/2011/12/car-still-runs-rough-after-tune-up.html

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2006 kia rio runs rough http://technoanswers.blogspot.com/2012/10/2006-kia-rio-runs-rough.html

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Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed? http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html

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Rough idle, staling and Erratic shifting? http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html

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These details will help.
Thanks.

If the engine runs good and is not rough then you may just have a defective O2 sensor. The sensor is located in the exhaust pipe just off the engine. See picture below.

What is model year? How long since a tune-up?
With idle issues, check and clean idle air system, see if it helps? Use a gage and check proper fuel pressure, key on engine off. On some ford vehicles, with everything off, unplug the maf sensor, where applicable, take the vehicle for a spin, if it does a lot better, have to check the maf system, that includes, sensor--wiring circuits--pcm.
The basics on a rough idle, is to check for a leak of some kind, fuel--egr--vacuum.
Positive fuel trim at low speed and load, the first thing, look for vacuum leak.

P1131 Lack of HO2S-11 Switch ,Sensor Lean
P1151-Lack of HO2S-21 Switch ,Sensor Lean
PO171- System to Lean (Bank 1)
PO174-Systen to Lean (Bank 2)

Fuel Filter -Plugged
Low Fuel Pressure
Evap System -Leaks
Leaks - in ducting,air filter to throttle
PCV -Leaks
Exhaust System -Leaks
O2 Sensors-worn out

A P0174 lean code for bank 2 is the cylinder bank on the LEFT (driver) side of the engine on Ford vehicles with a transverse-mounted V6 engine and front-wheel drive. This code is not set on four cylinder engines (no bank 2).
WHAT A LEAN CODE MEANS
A lean fuel condition may exist if the engine is sucking in too much air and/or the fuel system is not delivering enough fuel. If bad enough, a lean fuel condition may cause lean misfire, a rough idle, hesitation or stumble when accelerating, and/or poor engine performance . Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow (because the EGR differential pressure sensor that monitors EGR flow is faulty and is under-reporting EGR flow).
If the problem is not enough fuel, the underling cause may be a weak fuel pump, restricted fuel filter, leaky fuel pressure regulator or dirty fuel injectors.

check timing and set idle to 650rpm