My 2003 2.3L used to run bad... it had a lot of lag to it when i would try to accelerate. The check engine light was on so i got it checked, and the reading said o2 sensor high voltage or something like that... anyways, i purchased a new sensor (i researched, and found there is only an upstream o2 sensor, please correct me if I'm wrong), replaced it, and the truck ran WAY better, no more lag during acceleration, it was crisp. As i was driving home one day, i was accelerating up a hill, and at about 4000 RPM, the truck almost dies and starts sputtering. The check engine light started flashing, so i new it was serious, but luckily i was able to make it back to my house. When i got home, i looked under the hood and noticed that #2 & #3 spark plug caps had popped off the spark plugs. What I don't understand is what would have caused that to happen in the first place.... Is it a clogged Catalytic convertor, or is the o2 sensor bad.... Ive read different opinions and technical diagnostic possibilities, but man, i don't want to throw a bunch of money at a truck that I'm really going to have for a few more months. but I need to get it fixed in the mean time. Any input would be greatly appreciated.

 

Are you talking about the spark plug wires came loose from the spark plugs? Not sure what you mean by "spark plug caps"......

 

The caps popped off because you didn't secure them properly and they were lose.
When you pop the cap on the plug, it should have a slight snap. That means it's secure. If it does not do that, then the clip inside the cap is too big. You can possible look inside the cap and see the clip and take a needle nose pliers and crimp it a little bit to make it more snug.
I wonder if they are aftermarket plug wires. I only use Motorcraft sparkplug wires and they don't pop off...