I have a 97 F-150 with 141,000 miles on it. It has had a rough idle ever since I've owned it. Since about a month ago it has gotten really bad. Sitting at a stop sign or light it will sometimes feel like it's going to die. Feels like it almost locks up for just a second, it jerks so hard. Changed plugs, wires, and, coil pack to no avail. While driving at highway speeds, once it hit overdrive, the whole truck will shake. When it first happened I thought it was a U-joint. Check engine light finally came on so I took it to Auto Zone and had them put there code reader on it. Can't remember the code right off hand but they said it was a random misfire. Seems like a 0301 but don't hold me to that. I started running lucas in the gas and it hasn't helped. Tried sea foam and that's when the cel came on. What is causing this?

 

First off.. welcome to the site,Ive got the same truck...4.2 97 mine is an automatic lwb... to answer your question,id say there are a couple of problems here...first off,Id remove and clean out the IAC...Idle Air Control Valve.If memory serves its located on the top front of the intake plenum...These have caused issues in the past,and usually can be corrected by a good cleaning.
After doing that,if it doesent make a lot of difference,id suggest purchasing a OBDII code reader from any auto parts store. Its gonna be about 100 bucks,but its invaluable for todays vehicles,and can be used on 98% of the later models. Run it until you get a code,and read it yourself....
You could also need a good PROFESSIONAL fuel injector cleaning.
Replace the usual maintenance parts,fuel filter,air filter etc.
With that many miles on it(mine has 168,000) you might need to replace the converters as I did. It made a HUGE difference in performance,and spunk.
Hope this sheds some light on the subject..again...welcome to FTE!

 

Cleaned IAC valve. No difference!

 

I'd check close to insure there is no vacuum leak.
A loose or leaking connector or line has been known to cause problems like you describe.

 

I just fixed a similar problem yesterday, i had P0302 (cyl #2 misfire) and it was a bad fuel injector.

Ive been told there are 4 main problems that can cause a misfire.

• bad sparkplug
• bad COP (Coil on plug) - the wire that sends the spark
• bad fuel injector
• piston compression problems.

What i did to figure it out was swap a plug from a cyl with no problems with the plug from the bad cyl. and see if there was any difference and there was not, so my plugs were fine. Then my dad did something crazy and pulled the plug and put it in the coil (the wire) and put the sparking end close to a ground and let it the engine crank but not turn on, if you saw sparks then your wire and spark is fine. Honestly i dont know if that is a bad idea or REALLY bad idea, but it worked for me lol.

so at this point we have ruled out plug and wires, so then a neighbor of ours brough a cool tool with a pressure gauge that you can put into the slot were there spark plug goes and giving it crank it reads the pressure in the combustion chamber! was like 120 (not sure if it was MPa or PSI, probably was MPa) so the piston was moving fine. How to test car engine compression

So then at last was the injector. did the same thing as with the spark plug and swapped it with a good injector, and when i turned the truck on, all of the sudden it idled way worse than before, and driving was REALLY bad. So we figured it was the injector, got a new(or rebuilt) from a local parts store for 52 bux, put the injector in, and bam super smooth idle, no misfires, code cleared, and my truck had a pair again :P

anyway maybe you can try some of that stuff. good luck!

Also just some stuff I read, if you let that misfire keep happening, it could ruin your catalytic converter which can be way pricey to replace. If your Check engine light starts to BLINK, not just turn on but blink on and off, it means you are getting misfires and that aint good for the cat.

 

oh, forgot the mention p0301 is cyl #1 misfire, thats the first cylinder on passanger side (Closest to the front of the truck, passenger side) unless you meant to remember p0300 which is random cyl misfire, the computer doesn't know which cyl is misfiring.

 

Thought it might be the EGR valve. Took it out and cleaned, which it wasn't really dirty, and checked it with a vacuum pump. Tested good so I put it back on. Thought it could also be the O2 sensors, so, I unhooked all 4 of them and no difference. Probably shouldn't have done that but to late now. Changed fuel filter, no difference. Checked all sensors that I could find and all checked good with an ohm meter according to a Haynes manual. Only thing left is compression and an injector. Injectors look to be a real bi*#h to change. There is a sticker on the door that says the PCM was reprogrammed when the truck was 1 year old. Wonder if this might have something to do with it? I wonder this because the truck will run well over 100 mph. The needle hits the dash where the D for overdrive is. No I don't drive like this all the time! Had to know what kind of a truck I had when I got it. Just never know when you might need a little extra speed ya know.

 

Ran a compression check. All cylinders are 180 - 190 pounds. What should the compression be? Also noticed that the plugs are black as coal. They have a grand total 251 miles on them. That threw up a major red flag. Wouldn't that have to be the fuel pressure regulator? That would explain the excessive and I mean EXCESSIVE fuel consumption, the stumble on acceleration, and the rough idle. I don't have the stuff to check fuel pressure, but I'm gonna venture a guess and say that's my problem. What do y'all think? And , how the crap do you get to this thing? You can't even see it, and can just touch it over the back of the motor.

 

FIXED! 6 brand new injectors, a fuel pressure regulator, and upper and lower intake gaskets, and she runs like new! Needed intake gaskets really bad. There was a thick gray sludge that looked like anti seize in the lower intake. Also had a little puddle of anti freeze standing in the back of the motor. Gaskets on both sides of the lower intake were blown. One of the old injectors had a thin layer of crust on the bottom. Anyway it runs perfect now.