I just spent a crapload of money trying to fix my 2001 F-150 that had a rough idle when the A/c was on. First I had the injectors cleaned thinking that was the problem. Put a set of new plugs on for good measure. No Joy. Scope showed bad O2 sensor on passenger side. Chenged em both. No Joy. Finally, mechanic figured out the Ford in it's infinate wisdom put the computer and O2 sensor wiring harness under and next to the battery. After seperating the harness and insoecting the individual wires sure as hell found acid damage on one of the wires. Jumped it and checked the voltage and it finally checked out. So........if your F-150 is doing wierd things, before changing out any parts check the harness for acid damage. No good way to move the thing or protect it that I can think of. But if I had known this in advance it would have been a cheap and easy fast repair. Not a 4 day nightmare for way too much money. That Sequoia is starting to look pretty appealing.

My '98 was running like it had a fouled plug when it had about 78,000 on the clock. So, I round up a set of (pricey) plugs and figure I can change them myself. Wrong. Can't even get to the back 2, really. So I took it to the dealer. Exchange went something like this.

Service Writer (SW): What can we do for you today?

DzlBenz (DB): My truck has a fouled plug.

SW: No it doesn't.

DB: Yes, it does.

SW: No, it doesn't.

DB: Hey, pal, this ain't my first rodeo. I know a fouled plug, or at least a bad plug wire, when I feel it. And I'm feelin' it in my truck right now. But since my truck doesn't have plug wires (coil-on-plug ignition) I know it's not a wire. It's a fouled plug.

SW: No, it isn't. It may be running like a fouled plug, but that isn't what's wrong with it. In fact, I'll guarantee it. If we find a fouled plug, the repair is free.

DB: You're on.

So we go 'round back and hook it up to the Sun machine (or whatever), and at first, I feel vindicated. The mechanic says, "Uh, oh. #8 not firing." Actually, it may have been #7. It was one of the back ones. I felt pretty good. Then the bottom dropped out. "Dead coil." Shit.

What had happened was I had a pinhole leak in the heater hose. It was blowing steam directly on the coil for the back passenger side plug. (Is that #7 or #8?) Changed the hose in about 5 minutes, and the coil in probably less than that and I was on my merry way. Still, the whole repair was less than a C-note.

Moral of the story: There are so GD many wires under the hoods of these cars nowadays that there's no tellin' what's wrong with them when they start running goofy.

I hear putting a Chevy emblem on it will net you 20 Horsepower.

Lesson here, put it on the scope before spending money.   My local stealership gets $35 to hook her up.   Saved me money on the old merc, 155K or so it's needing the occasional sensor or plug wire every few years.  

Quoted: OBD-1 is your friend.

umm, 2001 is OBD2
it monitors everything quite closely and anybody who knows what they are doing should be able to diagnose what the problem is.

It's a Ford, what do you expect?

Quoted: My '98 was running like it had a fouled plug when it had about 78,000 on the clock. So, I round up a set of (pricey) plugs and figure I can change them myself. Wrong. Can't even get to the back 2, really. So I took it to the dealer. Exchange went something like this. Service Writer (SW): What can we do for you today? DzlBenz (DB): My truck has a fouled plug. SW: No it doesn't. DB: Yes, it does. SW: No, it doesn't. DB: Hey, pal, this ain't my first rodeo. I know a fouled plug, or at least a bad plug wire, when I feel it. And I'm feelin' it in my truck right now. But since my truck doesn't have plug wires (coil-on-plug ignition) I know it's not a wire. It's a fouled plug. SW: No, it isn't. It may be running like a fouled plug, but that isn't what's wrong with it. In fact, I'll guarantee it. If we find a fouled plug, the repair is free. DB: You're on. So we go 'round back and hook it up to the Sun machine (or whatever), and at first, I feel vindicated. The mechanic says, "Uh, oh. #8 not firing." Actually, it may have been #7. It was one of the back ones. I felt pretty good. Then the bottom dropped out. "Dead coil." Shit. What had happened was I had a pinhole leak in the heater hose. It was blowing steam directly on the coil for the back passenger side plug. (Is that #7 or #8?) Changed the hose in about 5 minutes, and the coil in probably less than that and I was on my merry way. Still, the whole repair was less than a C-note. Moral of the story: There are so GD many wires under the hoods of these cars nowadays that there's no tellin' what's wrong with them when they start running goofy.

Not to be a dick but why would you go into a mechanic's shop and tell them what's wrong?  If your already paying let them do their job.  I work on AH-64's and love when a Pilot tells me what wrong with it.  I often then begin the long and daunting process of amusing myself at there expense.  All I need to know is what it's doing wrong I'll take it from there

College education to break it
High School education to fix it

The scope (Genesis 3) showed bad O2 sensor. That wasn't the problem. The diagnostics cannot track a bad wire. It just tells you that there is one, but not where in the miles of wires and splices on newer model trucks. It was just luck that he found it. Sometimes the best diagnostics is the thing on your shoulders. And I don't care what car you have. All the late models aren't made to be worked on. They figure you go 150,000 miles before anything goes wrong and most people sell them before then. Before this I had a 94 chevy pickup that ran like a champ. At 165,000 miles I gave it to a long time employee as a bonus. He put another 50k on it until he loaned it to his wife who totaled it. On that truck anyone could work on it. Plugs were easy, hell, everything was easy. Now he bought an 02 that is as much as a bitch as my Ford.