The passages for the Exhaust Gas Recirculation (EGR) system can become restricted or clogged causing the Check Engine Light to illuminate. The EGR valve will need to be inspected and the passages cleaned.Google+
Car Problem Reports
Mazda Protege5 Check Engine Light Due to Restricted EGR System
Mazda Protege5 Problem
Average Mileage: 96,948 mi (45,000 mi - 149,000 mi)
Visitor, 2003 Mazda Protege5, 75,000 mi
I have the same problem as report #5.
I had the EGR valve replaced by the Dealer.
Still having problems with shifting/stalling issue.
Code PO300 Random misfire in one or more cyl. possible coil(s)failing...
I've replaced both coil packs, ign. wires and spark plugs.
Seem to have taken care if this issue. 1-4-2012
Visitor, 2003 Mazda Protege5, 80,000 mi
Mine seems like it downshifts itself and when it does..the check engine light flashes on and off and if I have to stop..the car idles roughly and wants to stall out. Having the air or heat on makes the problem even worse. I also notice it starts having this issue when the car has been driven for a while at a time. The EGR valve and throttle body have already been cleaned. Its going back to my mechanic who believes the EGR valve needs to be replaced entirely now.
Visitor, 2003 Mazda Protege5, 128,400 mi
Check engine light on. Rough idle @ stops. Not fixed yet. EGR Valve inspection scheduled.
As I come to a red light, my car begins to jolt at low rmps (100-200). The engine then dies on me and the check engine light is on. I have just replaced my timing belt, water pump, tensioner, battery, spark plugs, iginition wires, and transmission oil. Now the car stalls at every red light. It seems the service i have just done has made the problem worse! I will definitely check the EGR valve and hopefully that is my problem.