It's been a while so I feel bad only coming around when things go wrong…
She started running rough for a few minutes and then started throwing codes like crazy.
At first it sent:

• P0132 (Sensor Circuit High Voltage Bank 1 sensor)
• P1300 (Unkown Diagnostics trouble code), don't like that one
• P0303 (Cylinder 3 Misfire Detected)
• P0305 (Cylinder 5 Misfire Detected)
• P0307 (Cylinder 7 Misfire Detected)

and a "pending"

• P0125(Sensor Circuit High Voltage B)

After clearing codes and running in the driveway for a few minutes, just:

• P1300 (Unkown Diagnostics trouble code), don't like that one
• P0303 (Cylinder 3 Misfire Detected)
• P0305 (Cylinder 5 Misfire Detected)
• P0307 (Cylinder 7 Misfire Detected)

On top of the old

• P0455 (Evaporative Emission System Leak Detected (large leak) - that I've been meaning to get around to for way too long.

I was worried my attemted kludge repair of the air intake (that cloth over spring that attaches to the fender intake that rots out) had restricted airflow. Could this all be caused by restricted airflow?
I got the second set of codes running with the air box off.

Any hints appreciated. I'll probalby start with the wires and plugs, but that it's 3 out of 4 on the same bank is suspicious.

First Question: What is the cylinder numbering scheme?

 

Lots to unpack here, so here we go.

I'll go with the punch line first - change the upstream O2 sensor on Bank 1. Don't bother with wires and plugs.

A clue is that you have misfires on multiple cylinders appearing all at once. It would be unlikely for three plugs and/or wires to fail simultaneously.

First, let's set aside for now the P0455. That has nothing to do with how the engine is running.

Next, you asked about the cylinder numbering scheme. The odd numbered cylinders (aka Bank 1 - 1,3,5,7) are on the left-hand side of the engine, as viewed from the passenger compartment (the side with the ABS modulator). All the misfires you report are on Bank 1, which offers a strong clue. Plus, the P0132 code indicates a Bank 1 sensor problem.

I don't know what source you are looking at for the P1300, but the RAVE defines P1300 as "Random/multiple cylinder misfire detected - Catalyst damaging level of misfire on more than one cylinder". That's no surprise, given the separately-reported misfires on 3, 5 and 7.

The RAVE does not list P0125.

So that brings us back to the "what to do".

In my experience, and that of some others, multiple misfires on one bank are often caused by a faulty O2 sensor. The O2 sensor is the only engine management system component shared by a cylinder bank.

Others have written that a failed O2 sensor cannot cause misfires. Okay, but I live in Realville. My truck had multiple misfires on one bank. I changed the O2 sensor and the faults were cured. Others have reported the same.

Replace the Bank 1 upstream sensor and let us know what happens.

 

Oh! Well done Sir.
Excellent response.
Thank you so much. I’ll order one today.
I did the o2 sensors early in my ownership and remember some of them being maddening to remove. Fingers crossed upstream 1 is one of the easier (I think upstream was easier than downstream).

 

The most difficult, maddening thing about removing the upstream O2s is where the connectors are located at the back of the engine. I recommend reaching back there and sliding the connector off its bracket. You can then pull it out from behind the engine to disconnect and reconnect the plugs. Then, don't put it back where it was. Instead, leave it hanging loose but zip tie it to something to keep it away from the exhaust manifold. I made a small loop using some plastic plumbing hanger strap and mounted that on one of the nearby studs, as pictured.

 

i second mln01's internet diagnosis with a slight caveat.


i had the same issue and codes on one of my '04s. turned out to be a corroded pin on the O2 sensor plug driver's side.

so, that O2 sensor on the driver's side is definitely the one to look at. but inspect the plug and pins when you change the sensor.

 

Finally got the o2 sensor replaced. Defiantly the cause so well done there!
Took me forever to get the damn thing out - there’s just no space to get the tools under there.
now the new sensor is sending no information (still better then what the old one was doing).
I worry that I pulled a cable loose somewhere, but everything looks good. How do I test a sensor? Could just be that I got a dud? Really don’t feel like replacing it again, but better now then once it’s fused into the pipe.

 

Hmm... I usually suspect the car-side connector or the car-side wiring (which is... really annoying, sorry mate)

 

What brand sensor did you buy? I've had Bosch O2 sensors for my truck that were bad out of the box and others on this forum have reported the same. I haven't had to replace one for several years now (did I just jinx myself?), but next time I'm going with Walker, which seem to get good reviews.

You can bench test an O2 sensor using a small propane torch to heat up the tip of the sensor and a multimeter to measure the voltage produced. It helps to have a vise to hold the sensor while it's being heated, but you could probably use a pair of vise grips instead. There are many articles and videos on line about how to do this.

 

Shouldn’t be car side as the old one was causing all that chaos, so it was reading something.
unless of course I damaged it wrestling the old one out. Which is of course possible.
I’ve realized I’ve bruised my ribs by trying to get the plug sorted - so it’s at the edge of my reach, hard to be delicate.

Any way to test the sensor without removing it again? Such a huge pain in the proverbial.

 

Here is the answer for you old cloth air intake:
Works like a champ, cannot rot away or get chomped on by critters!