My car has been having what I feel to be a slight misfire. The check engine light comes on every so often but lately it comes on more. It turns off after shutting the car down and turning it back on. When accelerating up hills around here on the freeways it makes a bit of a "chatter". I scanned it and the code PO325 came up. I did a tune-up on it a few months back and noticed one of the plug wires was really rusty and corroded. I didn't change the coils and it seemed to be okay, but I'm debating changing them. According to some research it looks like it may be the knock sensor? The car has 115,000 on it and started this at around 110,000. I'm trying to figure out where to start before I start spending money on the wrong parts. Thanks.

The misfire that your feeling might be the PCM pulling back timing because its seeing an issue with a knock sensor.

Unless its because your going up hill and the strain on the engine is causing a chatter that the knock sensor is picking up, but that still doesn't account for the P0325 because that'* a knock sensor failure code...

https://www.gmforum.com/obd-ii-troub.../p0325-284048/

Unfortunately, the 3800 uses 2 knock sensors. One on either side of the engine block. The front sensor is easy to get to, but the rear sensor is a pain because the transmission sits right next to it. Which is another dilemma. The wiring for the oil pressure sensor and the knock sensor, sits right next to the passenger side driveshaft. I wonder if a wire has rubbed on it. BTW, its only a single wire going to each knock sensor.

you replace the plugs and wires and clean the coil terminals and put dielectric grease on it?

Plugs and wires were changed, dialectic grease put on all wires. The one coil that had a rusty wire on it was sanded down. I didn't notice any problems after the tune-up, this occurred a couple months later. I'll check the connections to the knock sensors.

I wasn't able to find the second sensor. I looked in the place mentioned in the thread posted by Mike1995. I can't quite make out all of the part number on the front one, but it looks to be #10456204.

There should be 2 sensors. The back sensor is protected by a heat shield and very close to the transmission assembly. I found this diagram on the net hope it helps.