I've had my 2002 Mazda Protege 5 for the last 100,000 miles of its life, and I love the thing. Recently it started acting strangely & stumbling at low RPMs + heavy acceleration. Within a couple days it could barely start and stalled immediately when the gas was touched. It threw an error code Po300 (random misfire).

I started researching everything that could cause this and found a long list of small things including but not limited to:

fouled plugs
bad wires
bad ignition coils
idle air control valve
EGR valve/tubing
vacuum leaks
PCV valve/tubing
computer issues
fuel filter
fuel pump

It ended up being the fuel pump relay. So that's good. But, now I'm definitely going to clean my IACV, EGR, and PCV because I didn't know these were good things to do before.

My question is this: What are other good/small/simple preventative maintenance things to do under the hood that a guy like me might not ever consider or think about? Things beyond changing the oil, checking fluid levels and tire pressures.

Thank you for your feedback! I'm also excited I found this forum as a result of this very minor breakdown.

 

Kudos for finding that original issue.
Don't just clean the PCV, change it! Clean the throttle body and MAF sensor. Replace the throttle body gasket.
Install a new cooling system thermostat as well as doing a flush and fill of coolant. Change the power steering fluid and brake fluid.
100,000 miles means it's time to install new ign coils.
Put a good fuel system cleaner in like Redline.

 

And a very common issue with the Protégé's is the intake hose which develops cracks through heat/cooling cycles and time.
Take it off completely, and spread out (flex) the corrugations in it to see if any cracks developing. If they are replace it, or your car will stand you at some point in time. There is no other permanent fix for these.
And too, as you suggest, with that many miles its a good idea to replace any vacuum hoses as well... same reason.

 

Also take your time and read the sticky "The Unofficcial user's Guide to the 95 to 98 Protege". Almost all of that applies to your car too.

 

Thought you were more thorough! You forgot to provide the direct link!
Here's the direct link to that thread made by our Protege guru Tanprotege, click on it: https://www.mazdaforum.com/forum/maz...%E9g%E9-31136/