Hi,

I own a 2001 Mazda Protege 1.6L LX. I bought it back in February and it was running fine. I started noticing that it would run kind of rough so I hooked up a OBD to it. I got the P0421-Warm Up Catalyst Efficiency code. I had already given the car a tune up (spark plugs, wires, oil change, air filter, transmission oil and filter change, radiator flush, and checked the battery, belts, and alternator). I thought it may have been the O2 Sensor so I replaced the one after the 1st catalytic converter. It didn't help. I took out the first catalytic converter and inspected it and it looked fine. I had the 2nd catalytic converter changed out at a muffler shop. No help. I used fuel injector cleaner. No help. I changed out the fuel pump because and screen because it failed on me (it was actually a short to the Fuel pump assembly, so I ended up replacing one of the connectors). Now, it will die sometimes when I turn it on, it idles for 5 seconds and dies. Then I turn it on again and it runs fine. When I am driving it it drives fine, it just shakes a lot when im in idle on drive. I took out the IAC and EGR valves and cleaned them with carburetor cleaner. No help. I hooked up the OBD again because my car had died on me and it gave me the O/D OFF blinking light on the dash. I got the following codes: p0102 MAF Circuit Low Input, p0103 MAF Circuit High Input, p0113 IAT High Input, p0123 TPS Circuit High Input, p1504 IAC Circuit Malfunction, p0506 IAC System RPM Lower than Expected, p0421 Cat Warm Up Efficiency below threshold, & p0300 Multiple Misfires. Now, I had been checking temperatures of both cats to make sure they were good. It seemed that they were both bad, and then sometimes I would get temp readings that they were good. Could it be that the 1st Catalytic converter is bad (even though it looked fine) and is causing all these problems? The rear o2 sensor I replaced produces the same amount of voltage as the one before the Cat (rapidly changing form .900v to .100v). Could it be the front Cat that is causing these problems? I don't know what to do. I don't want to fork up 300 bucks for a new Cat only to find out it was another culprit. What could it be? I wanted to also add that it misfires worse when I have the A/C on (the A/C light also blinks on and off when it is misfiring), like more violently. I have also noticed that it only is more consistent during the day when it is hot.

 

I would be replacing the MAF right now. Then, disconnect the battery, press the brake pedal for 5 minutes, reconnect the battery, start it up let it idle with AC OFF, for a few minutes, take it for a gentle drive & see how it goes.