I have a Mazda Protege(LX) 1.5 , 1996. It has 175000 miles on it. Of late, it has started giving me troubles. I do not know where to start. About three years ago, when the odometer reading was about 160 or so, the check engine light appeared. I took it to a garage. They reset the code. I did not bother to know what was the code about. After a while, It came back again. . The car started having rough idle. At a red light signal the rpm will go almost close to zero and then come back to the normal. This time I took it to other mechanic, he said the rough idle is because of bad throttle body position sensor. Though he did not get the code for it. He rather got the code for crankshaft position sensor. He changed the throttle body position and crank shaft position sensor. The rough idle problem was gone but crankshaft position sensor check engine code was still there. So his response was that crankshaft position sensor is not the problem and he put the old one back in the car and advised me that there is no problem in the car and I can drive with the check engine light on. According to him there might be some dirt in fuel injector. So use some fuel injector cleaner to clean the injector. I followed his advise. I drove for almost two years with check engine on. Occasionally, I will put the fuel cleaner, like Seafoam. For the last four months the check engine light has started blinking. Some time it will give P0303 some time P0302 other time it will be P0300. But of late it is giving p0300 only. The mechanic advised me to get the complete tune up done. So, we changed the spark, wires, rotor, cap, EGR valve, fuel filter. But this damn P0300 code is still there and the check engine light is still blinking. The mechanic says the fuel pressure and compression is good.The last time I took it to Autozone which was yesterday. It was throwing P0300 and P0134 (no activity in oxygen sensor). I do not have any other problem in the car. It runs reasonably OK except that I notice a very minor rough idle which I believe is because of its age. But this blinking check engine light with code P0300 is killing me.
Just to give more symptoms, I do smell some burnt oil when driving.
Just do not know where to go from here. Any help will be appreciated

 

p0300 is a misfire. I see you haven't changed your ign coil(s). Flashing cel is generally a misfire.
This can screw up your catalytic converter, especially when let go as long as you have.
I am not familiar with your car, but putting back your original crank shaft sensor is not a good thing.

READ: https://www.mazdaforum.com/forum/maz...%E9g%E9-31136/

Here is a list of generalized misfire code issues, don't ask me for specifics:

Missfires Can Be Caused By a Million and One Things,

Vac Leaks
Wiring Issues
Spark Plugs(Even Fresh Spark Plugs That Are Crappy Quality.... E3 And Such)
Ignition Coils
Alternators (Search EMI)
MAFS
Injectors
Injector O-Rings
Intake Gaskets
TB Gaskets
PCV Hoses
PCV’s
Malfunctioning EGR
Malfunctioning CAS
O2 Sensors
Aftermarket Intakes
Intake Hoses
Vac Lines
Timing Chains
Timing Chain Tensioner
Broken Cam Gears
Malfunctioning Cam Sensors
Incorrect Crank Gears(The I4 Has Like 40 Different Configurations For Whatever Reason)
Incorrect PCM Flash
Issues Within The PCM
PCM Wiring
Bad Diaphram Within The FPR
Issues Within The Fuel Pump
Dirty Fuel Filter
Dirty Fuel Lines
Pre-Cats/Poor Exhaust Flow

If the above gaskets/seals have not been changed, change them. Clean your MAF sensor, throttle body.
Change your PCV valve and probably that short hose as well.
Inspect the intake accordian tube for cracks. Inspect for vaccuum leaks.
Put in a good Fuel system cleaner: Red Line Synthetic Oil - Gasoline Fuel Additives - SI-1 Complete Fuel System Cleaner
Inspect wires. Re-set ECU after doing above.

Your car has way too much mileage for still having original ign coil(s) and O2 sensors, let alone the catalytics. I had a misfire on my car and it was poor exhaust flow. First they changed plugs, coil, injector fuel pump.

 

I forgot to add that coils, pcv valve were also replaced.

 

Today, I took out the Mass Airflow sensor and drove the car. The drive was a bit rough but check engine light even though it was on but not blinking. After driving for a couple of miles we scan the code. This time it was throwing code P0100 (Mass Airflow sensor) but surprisingly no random misfire code (P0300). The Mass airflow code is understandable because I disconnected it.
I guess my question is: Why did random misfire disappear when I took out Mass airflow sensor?
Is it possible that P0100 and P0300 cannot come simultaneously?
Could Mass airflow sensor be the source of problem (random misfire) in my case?
Any thought will be helpful.

 

I can imagine a way or two how a MAF could cause random misfires.
If the MAF is o.k. but a vacuum leak messes up the reading it could lead to random misfires.
Check for vacuum leaks.
If the MAF sensor is not o.k. it may lead to the wrong amount of fuel being injected and causing random misfires.

Check the fuel pressure. Did you ever change the fuel filter?

When you disconnect the MAF sensor the PCM will operate using program data rather than sensor data. That eliminates the two cases above.

Check if there is oil in the spark plug tubes. It would tell you that the valve cover gasket leaks. Oil on the outside of the plugs will cause misfires.

I assume that the mechanic and your parts store erased the codes each time when they scanned it. You can erase the codes by disconnecting the battery negative and stepping on the brake to drain all voltage form the PCM. When you get the CEl again have it scanned right away.

I bet a new EGR valve was not cheap. But it will only work when the EGR Boost Sensor gets a vacuum signal. That sensor sits on the fire wall passenger side and there is a vacuum tube going down behind the intake manifold where it connects to a nipple on the manifold. Pull the hose off and poke into the nipple with a strong wire. If you feel resistance poke through.
Also the EGR valve will only work when the EGR passages in the throttle body are not clogged. You could take the throttle body off and give it a good cleaning with CRC throttle body cleaner. The EGR passages may require B 12 Chemtool to get open and clean.
If you can get the car to run you could try a catalytic converter cleaning.
It will also clean deposits on the HO2 sensors and so on. I am not saying this will work but you can't loose much either.

By the way, I don't think your mechanic is on top of the game.

Before you came back with more questions read the unofficial user's guide that Noggin talked about. I wrote it just for you.
Then if you still have questions ......you are welcome.

 

O.k. I could not leave this alone.
An orange spark would indicate a shorted out coil. You would get a lower than spec resistance reading in either the primary or secondary coil.
The coil is an integral part to the distributor in this model. That means it is going to cost you some. I bought a Cardone re-manufactured distributor for about $200 at RockAuto.com. That was for other reasons though.

Here is a bit more info on spark color and such:Spark color to determine ingition coil performance - Car Talk