Hello everyone, I am new to the community and have got one for the mechanically inclined folk on this forum. After searching the forum to see if anyone has truck problems similar to mine, I have decided to post up what I think to be an insidious problem with my 5.4 F150. Okay so here it is, the truck will run fine and with no check engine light or symptoms of power loss. After driving for, let us say 40 minutes, I shut it off to pump gas or make a minor stop. When I try to start it back up, the engine will not idle and just shuts down. I can hold the gas pedal down to rev it into idle, but upon letting the throttle go the engine once again shuts down. This has caused me late arrivals to important events too many times and seems to be more of a problem in warmer weather. A mechanic diagnosed low fuel pressure and changed the fuel pump...did not fix the problem. I have the Haynes repair manual and enough wrenches and tools to try and tackle this on my own. Any suggestions would be greatly appreciated.

 

That could be 2 reasons both really easy.. clean your idle air control (iac) sensor located on back of Ur motor just look up on YouTube or your intake sensor located right behind throttle body

 

I mean air intake temperature (ait) sensor sorry

 

Thanks for the info. I will give those two sensors a look.

 

Welcome tell me how it goes

 

Update: I am starting my trouble shooting with the Intake Air Temperature (IAT) sensor.

According to the Chilton repair manual. The Power Control Module (PCM) should supply approximately 5 volts DC to the IAT sensor. "The PCM supplies approximately 5 volts (reference voltage) to the IAT sensor. The voltage will change according to the temperature of the incoming air. The voltage will be high when the incoming air is cold and low when the air temperature is warm (Chilton 1997 -2003 F150)."

I am reading 3.9 volts when cold and 3.8 after reaching normal operating temperature. I do not know if this is acceptable?

The sensor itself registers 30,000 ohms when cold and 20,000 after reaching normal operating temperature. This is good data and indicative of a well functioning sensor according to the manual.

I am not sure if this is the smoking gun. Any thoughts and suggestions? I will now check the idle air control valve for proper resistance and power supply.

 

Check your fuel pressure first. This is a very common problems for our 150's. My front pump (on my 96) has done the exact same thing since I got it. If I switch to my rear tank, the shudder and dying goes away. Test it once when the truck is cold, and then another after you have driven it to operating temp and shut it off. Restart it with the gauge connected, and see if you can recreate the problem while watching the pressure.