I have a 2003 Mazda 6S with 125,000 miles. Several months ago, my CEL started going on and off at various times. Then the car developed a missfire and the CEL light began to flash. I took it to the dealer for service. They said it had a number of codes, but the one that they thought was the problem was for a bad Purge Valve. They replaced the valve for a little over $300. A few days later the miss reappeared followed by the CEL. I noticed that the miss seemed to primarily appear at lower RMPs (under 2000) and with a slight load on the engine. I took it back. This time they said the code was for a "Lean Fuel Mix". They recommended a tune-up. So they replaced the plugs and air filter and cleaned the throttle body and fuel injectors. $230 later, I got my car back only to have the miss and CEL reapeare within a couple days. Took it back again and the same code came up for a Lean Fuel Mix. This time, they suggested changing both Oxygen Sensors. $300 later, I got my car back. I didn't even make it home before the miss reapeared. No CEL yet, but I only picked the car up last night. I am leaning towards a bad fuel regulator or bad fuel pump. The car doesn ot have a servicable fule filter. Any suggestions on what might be causing the problem?