Keep it or let it go?

[Steel City 06]

Note you can reset the PCM by disconnecting the battery for at least 30 seconds or so, which will clear the codes and the limp mode. However as soon as the issue is detected by the ECM, the error code will come back, followed by limp mode if it is bad enough.

Can be useful when you’re trying to chase a problem down. Usually each change you make, you’d reset, test, and see if the codes have changed. E.g., you swap the spark plug cables (at both ends) between 3 and 4 to test for a bad cable, so you reset and test to see if the misfire shows up on Cylinder 4 instead of 3.

 

[Steel City 06]

Another possibility here is that there may have been a mild misfire for some time, perhaps not often enough to throw a check engine light, but enough to damage the catalytic converter.

When the catalytic converter fails, it tends to go from a free-flowing exhaust to a straight-up clogged exhaust system that fights any exhaust gases flowing through. Usually not a big deal at idle or low power, but at high power or high RPM, the back pressure is so great as to block the engine from being able to take in enough air, causing numerous symptoms, often multiple random misfire or a severe lack of power.

That might also help explain the TPS code. If the ECM expects the engine to ingest a certain amount of air at a given sensor angle and RPM and it is actually taking in way less, the ECM might interpret that as an erroneous TPS or manifold absolute pressure (MAP) sensor value.

Clogged cats don’t always throw a code specific to the emissions system, so it can be hard to see at first.

The way to check would be to disconnect the converters and look inside. Or use a borescope and look through the bungs for the oxygen sensors. If the catalyst is not a perfect grid all the way through or appears clogged, the cat is probably bad. If it is straight up missing, it’s likely the debris went further down and clogged up something else like the 3rd cat (if equipped) or the muffler.

 

[Steel City 06]

Imho the only one there of consequence is the 303 cylinder misfire.

I'd get a compression tester from harbor freight for $50 or order one from Amazon. Super easy to pull the spark plug. Pull the fuel pump relay. Screw in the hose from the compression tester by hand and crank the engine for 10 seconds. See what the gauge reads.

The IAC might be relevant. I had a mouse eat my air filter. I didn't realize it until after I drove on a dusty road...went to knock it out and discovered most of it converted into a mouse nest...the throttle body was filthy. So check your throttle body and eventually clean your IAC... there's a write up in resources.

That dirt probably didn't do good things to my cylinder walls or rings.

-Mac

I’ve had a few run-ins with mice and squirrels that decide they like the taste of wire insulation, so they find the absolute most inaccessible spot and chew through a bunch of wiring harnesses.

Then it’s a cat and mouse game to chase down all of the resulting electrical gremlins…