i've posted a couple of times before about when i start my truck it jumps to about 1200RPM and when it idles down it DOES NOT STOP at 650rpm it goes down to 400 or 300rpm which makes the truck do one of two things stall or jumps back to 1500RPM and hangs for fifteen seconds and then comes back to 650RPM. So far in the past two months i've replaced these parts with Ford OEM replacements
-Idle Air Control valve
-throttle position sensor
-spark plugs
-spark plug boots and springs
-changed COP but didn't help so re-installed stock COP
-removed throttle body and cleaned it
-removed mass air and cleaned it
-checked EVER vacuum line and connection for leaks cracks
-did a vacuum test ALL NORMAL
-fuel pressure test ALL NORMAL
-gave up spending time and money and brought it to a local mechanic that i knoe he knows what he's doing. He checked all my sensors etc did all the normal Ford fix stuff and my truck still does the same fall and her face start up idle! He said he was going to find out something and call me back IF he finds something out. Its been two weeks and he hasn't called yet SO do i spend more money and try and let the local Ford dealer give it a try or what? I'm just sick of whats going on especially since my truck is NEVER off roaded i do nothing but maintain it and i have friends with the same truck who don't clean change oil or air filters take their trucks off road ever weekend and bury them in mud and water and they run like they are BRAND NEW!

 

I can share your frustration . It seems you covered many areas of potential trouble.
You had checked the fuel pressure . May be, run some tests on injectors , some may be malfunctioning (clogged). Try a good injector cleaner first .

Good luck,

 

i bought royal purple injector cleaner and did that anout three weeks ago and it didnt help anything. How do you check the injectors on a 5.4?

 

one thing i noticed yesterday when you turn the key on but not start the motor i can hear the fuel pump shouldnt it stop after five or ten seconds? Mine just runs and runs and runs.....

 

I had (well, 'have' if i was still driving it) this kind of problem with my 89 firebird with TBI injection. If you started driving before the idle reached its lowest point, which temperature depending could be anywhere from 20 seconds to over 3 minutes in the winter, then the idle would skyrocket back up OVER the normal high idle to like 2500 rpm, and you would have to pull over for at least 30 seconds to let it go back down... When it originally had the auto trans, I would leave work in the winter sometimes, get up to the first stop light and be trying to stop as my front tires werent moving and my back tires were burning out in the slush, etc... lol....

Anyways just saying, I feel your pain on this one, I NEVER figured the problem out. I even personally tuned that car a bit (burning new chips) and never could make a difference. Talked to the vast experts over at another forum.. some of those guys were building and now sell replacement ECUs, I mean they are good, but noone could help me... lol.

I finally just decided there must be something wrong with its brains.. a little corrision somewhere causing it to miss an important signal, who knows but I gave up on it. I dont know but maybe thats something a Ford dealer could actually test for you.

 

You are right , the fuel pump (with ignition on engine off ) should only be energized for 1-3 seconds . This needs to be further investigated ( is it a power issue-like grounding , or may be a bad pressure regulator not allowing the full pressure build )

Injectors require 2 types of tests . One is for PCM-power second for pressure/depressure test. Noid light will tell you if an injector is receiving power from PCM to start pulsing . An injector might be recieving PCM power but it can be clogged and unable to deliver fuel. The second test pressurizing and depressurizing test will tell if it is working OK . I have never done neither of these tests , but seen it done at YouTube.com auto repair videos.

Good luck,

PS. May be you can do a DIY test . While engine is running (if it is not idling by itself a second person needed ) unplug one COP plug at a time and try to determine if "no-change " in idling . This way , you may be able to identify some cylinder (s) to focus on . If you can determine some are not contributing to idling (and COP,plugs,boots are new) then you might take a closer look at those injectors .

 

the mechanic didnt charge me yet, he told me to drive it and see what happens till he found something out. Im going to stop there after work and tell him....... so now if he cant tell me i think it might be this i guess im going to have to spend another 95per hour to have the local Ford dealer look at the truck!

 

the F'ed up part is my truck is just a big street queen, oil and filter ever 3k even though a run full synthetic oil, fuel and air filter once a year, a clean the throttle body twice a year. do the spark plugs ever 50k, do a trans flush ever 30k and on and on. Yet like i said i have two buddies both with a 2003 and 2004 f250 ext cab short beds with the 5.4 that are lifted with 35" tires and they BEAT THEM TO DEATH! Ever weekend they go mudding and play in the Delaware river and try to pull out stuck deuce and a half's etc. My one buddy only washes his truck when it rains you open his hood and it looks like the motor has buckets of mud all over it! Yet when i get in their trucks they both start beautifully and idle perfect yet my "over maintained" truck wont start and idle correctly...............

 

wolf i did the DIY test like three times. I start the truck and go and unplug each COP one at atime. To my ear the idle doesnt change or the truck doesnt die etc. I did this also to each injector with the same results no change or anything................. thats not normal is it?

 

and if the fuel pump is only suppose to stay on for less than five seconds why does mine run and run and run untill i either start it or shut the key off

 

When you did the fuel pressure test did use a jumper for fuel pump pos signal ? You may have left the jumper installed or the relay is stuck or the fuel regulator is faulty.

 

Sounds like you need to go out with them once or twice and vent some frustration hahaha

First things first, you and your mechanic need to find why your fuel pump runs continuously. It shouldn't.
Second, have you tried starting it with your foot just on the gas pedal? Just to crack the throttle plate. Itwill idle higher, but you should be able to modulate it back down from there.

It may also be possible to adjust the stop screw for the throttle body to open a hair more to prevent the low idle and stalling. You might have to also adjust the TPS to read "shut" at the new position. This might not work with a newer truck though.

Good luck, don't give up yet!

 

Have you put a scan tool on it and looked at the live data to see what is going on when the idle acts up?

Have you checked fuel pressure while it is acting up?

 

I would take a close look at the Throttle Position Sensor, the the Intake Air temp Sensor, and maybe Coolant Temp Sensor.

 

run some seafoam thru the brake booster vac hose!!