Disclaimer: 90% of my forum posts anywhere are just getting my thoughts together, so this might not come across and a question or I'll end up answering it myself by the end.

2004 GT 6 speed with 88k. Plugs, coils, wires, replaced ~4k ago. MAF cleaned at the same time. All by the PO. Light isn't blinking or I'd be way more concerned.

Light first came on 3 weeks ago upon start up. No symptoms at all and nothing that seemed to set it off. Considering the new ignition, I decided to disconnect the better, brake stomp, and see what happens. Light stayed off for the last few weeks and 1500 or so miles. Just came back on today, again upon start up.

I wouldn't be posting if I wasn't baffled by the lack of symptoms. Power is certainly there and I'm getting 18 mpg no problem with my 50 mile round trip commute 5 days a week. Red line it merging from the on ramp a couple times a week. Besides that nothing abnormal or noteworthy.

Guess the next step is double check the connections? Just weird because it didn't have an issue before. Of course I can always clear it again, but rather just not have it in the back of my head.

 

^ Instead of guessing...you need to read the code that comes with the light. As a general rule the codes at startup aren't ignition related. Usually the only ignition codes you will get are misfires. Often startup codes are evaporative issues or other emissions related problems

 

Ah forgot to include that. Both times the light has come on, I went to advance auto, got it scanned, and that's the code that showed up. It stays on while driving and is still on after I shut her down and start up again later. I'll go to my regular one and make sure they're giving me all of them, but both times that's what it was. The guy today didn't want to even start the car for me. Not because of insurance, but because he never drove a stick.

Thinking out loud, would there be any difference with having a Mazda compliant reader from a dealership? P0301 isn't a mazda proprietary code, so can't imagine it would.

According to all the OBDII online stuff, 0301 can be linked to faulty inject or the cat, too. I planned on hitting it with techron right before my next oil change (within 500 miles) anyways, so that'll kill two birds with one stone.

 

Try cleaning the ESS. Then reset battery and 20 brake stomp.