2002 F150 SCREW; 5.4l
Truck runs fine when it's above (about) 10'F. Colder than that, and the idle won't hold. Truck starts fine, but idle won't hold...slowly drops and finally stalls. When driving, it goes for (let's say) 1/4-1/2 mile then idle slowly diminishes and truck dies. Restarts just fine; process repeats and repeats. Fuel consumption skyrockets. Restart after a few hours and it runs just fine. Throws no codes.

I'm thinking IAC or Intake Temperature Sensor.

What do you guys think?????

Thanks,

Jim

 

No codes; you cannot just begin to guess!
Likely the fuel tables are shifted very RICH as the cause of poor idle and stalling. It goes along with poor fuel mileage.
These things have to be looked at with a Scanner to verify the issue first, then the cause looked for.
Your doctor does not guess but verifies your health issues first, then the action to control or eliminate it.
Find a good diagnostic shop, let them see what's going on and why.
Goof luck.

 

Why would you think either of those items are at issue?

 

As I stated, it throws NO CODES to my scanner.

 

Because it seems temperature related.

 

consider looking at it this way.....
the inlet air temp sensor is MAKING A CHANGE when it gets cold!!!!! so....its probably doing its job?
like the running rich...."oh must be an O2 sensor?.....well...the O2 sensor is telling you it is rich.....doing it's job!

 

It "might* be the IAC valve but it's more likely a vacuum leak that appears when the thing gets "too cold" and something shrinks. Once it warms up, the leak heals until the next time. Note that the IAC is essentially a controlled vacuum leak that the computer accounts for in its fuel control algorithm.

You could try removing and cleaning the valve, your only cost is some time and potential frostbite. I've found that cleaning them is a pretty temporary "solution" and replacement is usually needed if they get sludged up and get sticky.

 

Cold starts are>>>>Rich<<<< by design and needs intent, and will cover up faults until the engine begins to heat.
Then the fault begins to affect drivability when the rich condition is pulled back by the PCM.
If the condition persists, idle smoothness and stalling plus fuel mileage affects drivability.
The total system involves the Thermostat, cylinder head temperature sensor, intake air sensor, and both Ox sensors plus proper IAC action under both cold and hot operating conditions..
No codes demands you look at the data with a Scanner to see what is out of 'normal' operational 'ranges'..
No codes does not always mean no part of the system is near being out of limits.
Either use a Scanner or have fun and spend by guessing and still not get results.

 

Just wondering, if its dying while idling in gear? Or in park/neutral?

 

In gear.

 

Still having this issue. Any new thoughts/theories. guys?

 

Your not providing enough reliable information. Bits a pieces are difficult to put together.
There is really no difference between cold start and hot re-start except the >>temperature.
All the same sensors and functions are used.
If the motor smooths out when fully heated, the system is not sensing the cold start temperature in the proper manner.
This is not theory but how the system works.
You must offer enough information to point to a likely cause.
A. Does the motor go to high idle on cold start? Yes or no.
B. Does the temperature gauge come up to normal after warm up? yes or no.
C. Are you getting any heat from the heater? yes or no.
D. Have you checked the harness to the cylinder head temperature sensor yes or no.
E. Have you checked the plug up at the Mass Air meter and Intake Temperature sensor in the AIR TUBE between the air filter and the throttle body? yes or no.
F. Have you cleaned the Intake Air controller? yes or no.
These are ALL involved in cold start.
.
Hot Idle:
1. Is it smooth? yes to no.
2. Does the motor idle rough or stall when hot? yes or no.
Any yes answers indicate a different or additional fault.
We must know these answers in order to help you.
The issue you have is 'nearly' impossible not to have a code or be undetectable using a Scanner.





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