The Unofficial User’s Guide to the Mazda Protégé, 323 and similar models
This thread is intended to compile a list of issues and their solutions with the Mazda Protége, 323, MX3, 626. If you know of other solutions to issues with this model please post a reply or send me a PM.
Do not post questions to this thread.
While the following is based on my observations on a ’98 Mazda Protégé many pointers can be applied to other normally aspirated 4 cylinder models as well.

Mazda Protégés are very reliable grocery getters. However, they do need some maintenance and repairs. Here is a list of common problems and fixes.
Engine:
Maintenance: Most people should adher to the severe duty maintenance schedule in the owner's manual. Oil and oil filter changes every 3000 miles. If you use synthetic oil you can extend the the interval but you still need to change the filter because it gets saturated.
Coolant changes every 2 to 3 years are needed because electrochemical processes don't stop when you stop the engine!
Mazda puts too much trust in its PCV systems: replace the valve every 2 years, even though it is not listed on the schedule.
Other items and repairs: Common issues are a failing catalytic converter and rough idling.
Sometimes the idle speed drops way low before recovering. It is a good idea to start with a cleaning of the MAF sensor, throttle body and performing a “Seafoam” treatment. If in addition you follow the instructions for “Rough Idle and P0171”, “EGR”, “Misfiring” the almost-dying-idle condition should be cleared. Using midgrade or higher octane fuel also helps with drivability at low rpms.
Rough idle and P0171 Lean condition bank 1: Look for vacuum leaks. Prime spot is the ribbed section of the air intake hose. Wrap it with duct tape or replace it. The lower intake manifold gasket is another hot spot for vacuum leaks. Replace it.
EGR system: the EGR boost sensor gets a vacuum signal from the intake manifold. The nipple at the intake manifold may be clogged. Follow the vacuum hose from the EGR boost sensor down behind the intake manifold, pull it off and poke into the nipple with a strong wire. If you feel resistance push through. Replace the hose.
Remove the EGR valve and clean it out. Use throttle body cleaner for the throttle body and B-12 Chem Tool on the EGR passages only. Replace the gasket.
Some cases of a cracked exhaust manifold have been reported. Replace.
Misfiring: replace spark plugs, wires, cap and rotor. I don't trust these ignition parts if they have 35K miles or more on them. If misfiring persists it may be that oil leaks into the base of the distributor covering the optic timing sensor. Remove, clean and replace a seal. If there is oil at the bottom of the spark plug tubes replace the valve cover gasket set.
P0420 Catalytic converter insufficient warm up efficiency: There is probably no way around it: the cat is dead. You may try cleaning the catalytic converter using 1gal of lacquer thinner (not paint thinner!) in half a tank of gas and driving it for an hour. Or remove the catalytic converter and soak it in soap water over night. Chances are you need a new catalytic converter.
Timing belt: the 1.5L engine is a non-interference engine. A broken belt should not damage the head or the pistons. Timing belts should be replaced every 60K miles. Replace the tensioner and cogs at the same time in the interest of reliability. Also consider replacing the water pump since you are there already.
Drive belts: The drive belts are flat, ribbed serpentine belts. They need to be tensioned properly to avoid squealing. If a properly tensioned serpentine belt squeals the alternator pulley should be inspected. It may have been polished so smooth that the belt slips. Roughen the surface with sand paper.
Brakes:
The brake fluid should be completely replaced every 2 or 3 years. The fluid attracts moisture and the new fluid has additives that keep the rubber seals in good condition.
Until ’98 most protégé’s are equipped with front disk / rear drum brakes. If your car shows reduced brake performance, reduced fuel economy and delayed shifts (if automatic) it is worthwhile to check for sticking brake calipers. There may be rust and corrosion on the sliders and in the mounting hole for the sliders, behind the rubber bushing. The rust presses on the rubber and keeps caliper from sliding back off the disk. There could also be rust under the anti-rattle shims at the pads. Take apart the assembly and remove rust with wire brushes and sandpaper. Apply a thin layer of high temp disk brake grease to all cleaned surfaces and reassemble.
When you get new pads read the instructions. Some pads need grease others have anti-squeal backing that will be damaged if you apply grease.
If the parking brake does not release the drum brakes need to be taken apart. There is an actuator bracket with a self-adjusting mechanism and parking brake lever attached to it. All movable parts may be sticking caused by rust and brake dust accumulation. Clean the assembly with brake cleaner. Loosen all sticking parts using PB-Blaster and tapping with a hammer. When they move freely apply a small amount of brake grease or anti-seize compound to the joining surfaces.
Check if the parking brake cable equalizer in the center of the car, above the exhaust pipe is moving freely. You may free it up with PB-Blaster and apply a dab of high temp grease.
Power locks: If it takes a few hits on the power lock button to make all locks open the lock actuators need some cleaning and lubrication. Remove the door panel spray MAF cleaner on the mechanical parts and apply some dry lube.
Blower: if the blower does not work at every speed it is most likely a failing blower speed switch. A handy person may be able to take the switch apart and make it work better than ever by adding a small spring and ball at a position 180* to the existing spring and ball. In most cases the blower resistor is not to blame. Also if the blower switch fails the A/C may refuse to work.
Horn: If the horn keeps blowing then the foam layer under the horn plate in the steering wheel is deteriorated. You can replace it with foam from the fabric store.

 

Please don't overlook the dreaded PCV valve as Mazda does not pay much attention to them.