I am pretty sure this has been posted before. I have tried all that I can afford and can not go into anymore dept trying to figure out what the problem is. I have a 2001 F150 4.6L Supercrew. The truck has 260,000 mi. In the last 8 months it has started and gotten worse with a horrible rough idle and when I stop at a sign or red light, it will idle down and die. I have trouble starting it when the motor is warm but starts right up when it is cold. The oil pressure sensor is going out as well, will that have anything to do with the rough idle? I always check the oil and maintain regular oil changes. I have replaced the fuel filter, IAC and vacuum lines behind the intake. Fuel pumps are expensive and as I am pregnant, I cannot drop the tank to install a new pump. Is there ANYTHING else that I can try in the driveway to possibly help?

 

Are you absolutely the sensor is going out? or is the Oil pressure actually dropping out?
With this amount of miles showing,Im pretty sure bearings are worn,causing a low oil pressure situation.I have doubts that the problem is the fuel pump.Normally when they fail...they fail.
You might have a professional injector cleaning done also.This may help.

 

Oil pressure light and needle fluctuate; sometimes I dont have a problem with it and some days it just does not want to work properly until the truck is warmed up. The fuel filter was nasty and slugged when it was replaced. I ran 30w for the longest time (ex-husband, ase cert mechanic suggested that in Texas it would be fine) recently switched to 5w20 and now have a slight knock as well. I have been reading that this could be due to the idler pulley? I do know it is not an O2 sensor or anything to do with the exhaust. I do have a bad bad habit of running the truck on empty due to paycheck to paycheck syndrome...

 

Look to the DPFE and EGR open situation. Remove and clean the EGR. You can test it by putting vacuum to the EGR idle should go from smooth to rough back to smooth. Texas 5w20 oils are more about mileage for the manufacture fleet than anything else. Sounds like your X isn't such a bad guy to listen to. A 5W30 synthetic blend will protect your old engine just fine in Texas summer heat. Age more than anything will do damage. Wear parts just fall apart when they age. Much like we do. Even Ford recommends it for its Ecoboost cause the motor works harder. LOL

 

While I do understand the paycheck to paycheck thing,you need to remember that MOST of what keeps that expensive fuel pump cool is fuel.Running it low can cause overheating of the pump,and failure.
Personally,It sounds to me like a rebuild is in order... There is also a screen in the tank designed to catch any "big chunks" before it gets into the fuel rail.If your original filter was "gunked up" chances are there is indeed more in that screen.Fuel rail pressure test should show any pressure abnormalities.
PT has a point.....EGR can cause idle issues,especially if the pintile,and seat are carboned up.Cleaning it may help,but dont expect miracles.

 

Not that this is going to help much at this point but the running of the heavey oil in those earlier years did not help out the cam chain tensioners that now may be starting to make noise in the front of the motor.
They are replaceable.
Going to the lighter oil now makes it worse after the wear has occurred.
.
As to oil pressure, the sensor is just a switch that operates at about 6 lbs pressure to signal the dash that there is pressure there but not tell you how much. The dash gage is just a meter that is circuit designed to move to a location and stay there after the pressure switch closes.
Best thing to do here is put a pressure gage on and check what you have hot and cold and make a determination of bearing/pump wear. In this mix, the cam chain tensioners are dependent on oil pressure. If the pressure is low and there is wear, the ;chains; will become a source of noise.
If you should find oil pressure at the 6 psi level or lower hot idle, your just running on borrowed time until full ,lfailure results and considering the cam chain tensioners posibility. The wear by products from the chain tensioners likely lay in the oil pan.
In a good motor, the cold pressure can be as high as 75 psi. cold oil idle.
When fully hot at idle should be over 10 psi at least and preferablly at 20 psi.
As reference my truck is an 02 with 168,000 and use gages full time so I see it every day. The motor has never had any other oil but 5w20 all year around and towed gross weights of 12,000 lbs. for awhile.
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As to idle, remove the IAC controller right on top of the intake near the firewall. It has an electrical connector .
Use Throttle body spray cleaner inside till it comes out clean and the spring loaded pintel moves freely.
Also clean the inside of the throttle body and plate while holding it open from the outside. These items control idle.
. Hopefully this will solve the idle issue and resolve the cold and hot starting issue.
Let us know how it goes.
Good luck.