yeahford

hi, i have a 98 f150 4.6l auto trans 183,000 miles. im looking for some ideas to make it run better. first, it idles high in or out of gear. Second, it runs kind of sluggish like it revs up higher than it should have to to go faster. third, it sort of shudders under acceleration. lastly, bad mpg. i am getting lean fuel mixture codes.

i started out by cleaning the egr valve and welding the egr tube back on the the manifold cuz it was busted off, somewhat but little performance improvement.

next i changed the fuel filter. once i did this the truck ran amazing. next day, go to drive it and it ran the same as before. i changed the fuel filter again after that and there was no differnce. this is the part that really confsues me

the next thing i did was replaced the egr solenoid. once i reconnect the vacumm hose back to the top on the egr valve the truck started idling very rough and stalled out several times. i put the original solenoid back on.
after all of that, i replaced the fuel pump and noticed a little bit better performance.

i have checked all of the vacumm hoses and pcv valve that i could see. tested the voltage on the dpfe.

any ideas would be greatly appreciated. or maybe the truck is just getting old

udderbrudder

The shudder makes me suspect a cylinder misfire under load. This would also expllain a lean code. I think you need a tune up. Plugs and wires should improve things.

yeahford

what type of plugs would you recommend using?

Fixitman

Just my 2 cents worth:

Did you get correct voltages at DPFE? Hi Temp hoses were clogged on mine.

1. Clean throttle body EGR ports. clean Throttle body butterfly too.
2. Check IAC - could be allowing too much air in
3. EGR valve sticking open?
4. Vacuum canister leaking
5. Plastic vacuum line cracked or broken

+1 for udderbrudder: check plugs and wires and ignition modules (2 - front of engine both sides)

I found Motorcraft parts are the way to go on these engines. Tried other plugs, wire, sensors etc. Motorcraft is what I came back to to fix a problem. No I do not work for Ford.

As I said: just my nickles worth. Your mileage may vary

Mr.Bones

Motorcraft plugs, i would clean MAF as well as the throttle body. Only use throttle body cleaner. Carb and choke cleaner can damage the intake as well as the body and butterfly. X2 on ingition modules.

Warspite

+1. Don't go with 3rd party plugs - non-nickel ones are prone to getting spit out of the head (literally). Also, check the elbow and hose going from the throttle body to the valve cover PCV valve. Common failure and vacuum leak source. These and the above posts are the most common causes/fixes for lean codes and high idle. If you have an aftermarket cold (or hot) air intake, that too can contribute to the lean codes as well.

me1234

Carbon Deposits?

https://www.f150forum.com/f12/carbon-deposits-170358/

yeahford

hey guys. i changed the plugs and wires. no improvement was shown, the old plugs looked to be brand new still.