...when I accelerate. Really have to feather it, even does it when running cruise control. Plan on replacing plugs, wires soon. Any other thoughts on the possible culprit? I have recently run a bote of sea foam through it.
Sounds like a fuel filter or fuel pressure problem. Any codes? If it is missing you should have some PO300 codes where the last digit indicates the cylinder(s) with the miss. Gary
Which engine 4.6-8, 4.6-6, 5.4-8. 99 versions will not indicate cylinder only bank. Takes a min of 10 % loss to trigger codes. How many miles. Now on to some quick repairs replace the vacuum lines to the pcv valves. In the case of the v8's one comes off the front of the intake manifold and the other off the back the rubber hose portions break down with age, they are covered with a foam like insulator as well so squeeze test is of no help, rear one is most likely culprit. Dealer only item as these are preformed. Next if a 4.6-8 and 6 replace coil packs , plugs, and wires; 5.4 does not have wires as it is a cop unit so it is just coils and plugs. ( just replacing the plugs seldom resolves anything, also if those are the original plugs they are a 3 piece design, I do not recommend an amateur to try and replace these as they tend to break apart causing further issues) The next area to look at is the egr assembly, they tend to rust out right at the exhaust manifold as well as the solenoid getting gummed up or just plain frozen. If you haven't cleaned the IAC sensor do so or replace it as well. My guess would be a vacuum leak as the main culprit in the pcv circuit. 100k miles was/is the recommended plugs, wires, coils replacement interval. I had a F150 99 4.6v8, and still have a F350 99 v10, the above is my experience with these. I can go a lot further if needed but would suggest a bit of research on the ford F150 forums.
Recent seafoam... definitely replace the fuel filter! I trashed a carb in my '86 F250 after running seafoam in the tank. Now it has an external one added which is easy to see and change.
Fuel filter for sure, and if that doesn't cure it, start looking at the ignition system per Chris's post.
Another vote for what Chris said - sounds like a vacuum leak. I don't know much about Fords, but I had the same symptoms on a GM vehicle when the vacuum line to the MAP sensor cracked. The lack of vacuum to the MAP sensor made the ECM think the engine was running at full throttle. I was 130 miles from home, in a snowstorm, and had to drive heel/toe style for 10 miles to an Autozone. One difference between my symptoms and yours was the CEL was lit in my car and thats what pointed me to the MAP sensor/vacuum line.
Depends if ford still used a vacuum actuated cruise control in 99 or if it was electronic. In my case cruise worked fine. Until I got off the highway and the engine went down to idle. Troubleshooting driveability issues was never my strong suit, unless it was a pre computerized vehicle.
Ok,'we'll when I see the parts mistress I will get the plugs, wires, and fuel filter that it's due for anyway. If that doesn't fix it, I will look deeper.
Vacuum leak would run better the harder you get into the throttle. No issues at idle..... Likes to be driven gently.... Right?
I would throw clogged cat into the possibilities, but I'd imagine that would throw an O2 sensor code before drivability was affected.
My 5.4 did this all the time. My issue was coil packs. The hood seal is shoddy on the hood and the 4 cylinders (2 on each side) get moisture dropping on them whenever it rains. Which prematurely wears them out. It very well could be vacuum related as well. A quick stop at an Advanced Auto/Auto Zone should tell you if you have cylinders misfiring. If it hasn't been done in a while, a new fuel filter is always a good thing. BTW- If it is coil packs, I bought a V-10 pack on eBay (coil packs are the same on all the gas truck engines) if you want to replace them all and put 2 extra on the shelf. Or just replace the 1 or 2 bad ones.
I could also add that you don't always see a check engine light when a code gets thrown. There may be info for the scanner still.
