Bad plug wires?

My father drives a 2000 4runner 3.4l 2wd 165,000 miles. Ever since he's had the truck, it has felt really underpowered getting on the freeway / passing, and is a little hard to start sometimes. Nothing like my brothers 4runner or my Tacoma. So we decided to replace the spark plugs, fuel filter, clean maf, etc. Performance didn't change. While removing the plug wires, we noticed that one of them looked a little more discolored then the others. Thought it was normal and just put them back. A month or so later the cel came on. Can't remember the code but we cleaned the maf and reset it.

Now 2 months later the code comes on again. PO171. Everything feels like it has before. For the past few months, there has been a few times where the truck ends up dying just idiling in the parking lot for no reason.

We we wondering if this is all related to the plug wires. Could anyone chime in.

 

If the truck has 165,000 mile on it I would change the plug wires whether they were the problem or not. How much could a set of wires cost? Usually if a plug wire is bad you would have a misfire in one of the cylinders but like I said, how much could a set of wires cost?

 

I ordered some NGK's off Amazon a bit ago for $29. Going to see if that helps fix the problem. They probably needed to be replaced anyways as they look to be the originals.

 

P0171 - Fuel Trim System Lean Bank 1 (which can mean that the O2 sensor is bad or the MAP is bad..... this taken from toyota-4runner.org

 

How are you supposed to know which of the oxygen sensors is bad besides disconnecting it and testing the ohm's. Isn't their 2 sensors? Wouldn't it be throwing a different code?

 

Pre cat does the fuel adjustments. Post cat tells the cpu if the cat is functioning.
You should get a fluctuating voltage around 1vdc from the pre cat. Post cat should be steady.

 

There's different codes for the different O2 sensors. No need to test them unless you want to be sure it's really the sensor and not a wiring issue.