4.2 V-6 seems to have a common problem
 

After reading other postings in these forums, it seems that I am not alone with the problem of my engine running rough. I also noted that there were many similar descriptions as to the problem and many more possible causes.
Here are my details.
1999 4.2 V-6 130,000 miles. Changed plugs and wires. Problem still exists although I did note a fuel mileage increase.
When cold, the engine runs fine. Once warm, as I try to accelerate, it stumbles as if it were a carburated engine with no accelerator pump, then continues to misfire throughout the shift changes to freeway speeds. If I floor the pedal, it is not quite as noticable although it still misfires.
OBDII code reader comes back "Pass" with no error codes.
If it were fuel pressure, it would happen when cold also.
A minor vacuum leak should not cause such noticeable misfires, and at any rpm.
Would a MAF sensor be the cause even though it comes back with no error codes?
I now am inclined to think that the culprit is going to be the Catalytic converter being somewhat plugged after 130,000 miles. Am I wrong in my thinking?

Have you ever changed your o2 sensors.

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Contrary to what most will tell you, 02 sensors do not need to be changed regularly. only when malfunctioning. I am an Industrial Electrician/Instrument Tech. and we use 02 sensors in many types of furnaces. When we have trouble with them, we simply remove them, heat them with a torch until nearly red, then blow them off with an air compressor, and put them back into service. Should they fail our testing, then we replace them. I have done the same on many vehicles, expecially those with carboned 02 sensors due to rich conditions and they work perfectly after cleaning.

So, to answer your question about changing the 02 sensors, no, I have only cleaned them. They appear to be doing their job quite well and I see no need to replace them at this time.

Well clean away. Good luck.

Yes, a MAF can cause what you report. But, I'd check the fuel pressure, consider the fuel filter if it is old and moldy, look at the air filter, just general maint items. You can clean the MAF if it is just fouled.. and it doesn't take a lot of gunk to make it misbehave.
Re the O2 'disagreement': Of course, Bosch wants to sell you a new one. They generally fail altogether, or start to get lazy. Lazy meaning that they are a little slow to warm up, and a little slow to respond to the delta-O2% in the exhaust. A good mech can scope them and know w/o removing and cleaning. A good run down the highway *should* clean off the carbon, but Murphy does collect his pay regularly.
Just read a web site on the O2 sensor this week. If I find it I will post their address if you are interested.
tom

Thanks for your input.
After trying everything I could think of, I went back to the beginning. I replaced the plugs, which didn't help. I had previously installed new plug wires about a month before, but on the off chance that they were bad, I again bought new wires.
Bingo!
My power is back, no missing, and milage has doubled.
Go figure!