i have searched and found stuff similair to my problem but not quite. my problem is 3 days ago sitting at a light my truck idle would drop to 200 then go back up that went away. today it has occured frequently when im at a light my idle will drop go up then the engine will die what is causing this a bad fuel pump or what. truck is in my signature

 

It could be caused by a number of things. If for some reason you think it is the fuel pump, then you will have to connect a gauge to the fitting on the fuel rail and test it. Pressure should be about 32psi at idle and increase to about 40psi under full throttle.

Your symptoms could also be caused by vacuum leaks, sticking IAC solenoid, dirty throttle body, bad sensors, etc.

You need to run a EEC test to see if there are any codes in the PCM that may give you a clue as to the cause of your symptoms.

Jay

 

The first thing I always check on a Ford idle problem is the IAC valve. But yeah, it could be a multitude of things and you need to check for codes like fireme said.

Always nice to have a Haynes manual on hand. It'll give you code pulling procedure and info on how to test various sensors manually.

 

only codes are 617 and 626 which are both trans codes