My check engine light came on in my Protege. O'Reily's read the code for free and it said EGR valve. I had cleaned it a year ago and since I used anti-seize on the bolts and 4 screws, it was easy to take the EGR valve off again. It was kind of dirty. I cleaned it, reset the check engine light, and everything was fine. Later that afternoon in heavy traffic, the check engine light came on again. When I got home I checked all of the hoses and connections and they were fine. When I did the EGR cleaning the day before, I cleaned the valve cover as I always do. As I was inspecting the engine after the check engine light had come back on, I noticed a trail of engine oil from the oil filler cap down the valve cover and it was hitting the front exhaust manifold cover. I had been smelling oil sometimes when the engine heated up. I removed the cap and saw that the rubber insert gasket in the cap was very flat and did not seem to be sealing properly. I got a new cap for $5.99 and put it on. The check engine light has not come on since. So maybe, if you are lucky, the check engine light and EGR code may mean you only have to take off the oil filler cap, clean it, clean the valve cover surface where it fits, tighten it real good, reset the check engine light, and you may save a lot of trouble and money. If you are leaking ANY oil from that cap you need to replace the cap since they are cheap. I am not sure about the Mazda, but other cars I owned did funky things when they had a leak in the valve cover or related hoses. Good luck.

 

Thanks, moozmooz. I will put this hint into the Unofficial user's guide!

Don't get a stiff neck from driving in reverse, if you know what I mean!