Code P0401 - changed EGR valve but still having problems at idle
 

Hello all, I have a Mazda Protege ES 2001, 2.0L and I had problems stalling at idle. The car would shake a lot and die when I stopped. It took a few days and the check engine light came on. The mechanic scanned it and got the error code P0401. He changed the EGR valve, since it usually is the problem on the Mazda Protege of those years. He told me that the new EGR valve is modified so that it won't have the same problem again. However, my car started to show similar problems only 2 days after he installed the new EGR Valve. My car is not stalling yet, but it's idling very low and my car shakes when I am stopped and sometimes the idle is going up, then down, as if the car is breathing (I don't know how else to explain it, it's doing it with a stable rhythm). What is the normal idle rpm for Mazda Protege ES? Can it be that my idle is not well adjusted?

I went back to the mechanics and they said that it might be because my intake was dirty and the dirt is maybe going into the new EGR valve and cloogging it. They wanted to put something to block the EGR valve to see if the new valve was the problem. I thought that was strange so I didn't do it. Now I don't know what to do... Can I clean the intake myself? Can it be some other sensor? I tested the MAF sensor and it seems fine. Thanks for your help!

My older protege and most likely yours as well has a thing they call EGR Boost Sensor. That is a bad name for what is truly a MAP sensor (manifold absolute pressure sensor). It sits on the firewall at the passenger side and a vacuum hose runs down and behind the intake manifold. The nipple there may be clogged with carbon deposits. Take the hose off and poke with a wire into the nipple you may feel some resistance. You have to poke through that resistance to remove carbon deposits.

That EGR boost sensor tells the computer when to operate the EGR system and when not to operate it. It shouldn't operate at idle. But when the vacuum line is obstructed the sensor can't tell what's happening.

I cannot be sure that this is your problem but it is worth checking, and cheap enough too.