Good morning.

I seem to be having a reoccurring p0300 with no other symptom codes. Upon cold start there is a brief stumble before smoothing out and returning to normal no issues after that. Changed the spark plugs and inspected the wiring over the valve cover.
I've read to clean the EGR maybe I need to try this on the weekend.

Any information would help

07 CX7 155K miles
Original chains and tensioners to my knowledge.

 

Generally speaking we that is Diagnostic Technicians hate PO300. They dont really help solve a problem. P0300 is a DTC because the ECU has no set programing for likely anomalous or combination of issues that are not bad enough to activate a more directional DTC to resolve the problem that caused issues. You need to clear the DTC and check and re-set the monitors. Note everything you find in the monitors that is not in readiness. Go drive a couple of complete engine cycles then see what happens and hopefully you will get a more helpful DTC to start trouble shooting. There is no set diagnostic tree so just about anything can activate a P0300 DTC on most all makes and model vehicles.

 

Thanks for your reply. I cleared the code and in 2 days it came back. Still only p0300 and still only stumbles upon cold start up and then everything is normal.

 

You need a scan tool that can monitor / record individual miss-fires on each cylinder over multiple drive cycles.

Mazda's MMDS software does this, it will record each cylinder even if you don't get P0301, P0302, P0303 or P0304 DTC's.

 

Thanks for this info.. any recommendations as to where I can get this software without going to the dealer for diagnostic?

 

I don't know, sorry.

 

Had the same code for over a year. Would clear it and wait and see if a specific cylinder was the problem. Turned out to be the timing chain was getting stretched and as it got longer the camshaft gears were getting out of sync until the engine blew.

 

This was my fear. I haven't found any other codes that would give me a different route. I even checked the harness that runs over the valve cover.

Time to source the parts to do the timing.

Thanks for your reply.

 

P300 means not DIY friendly for diagnostic work. If it will not clear you really need to take it to a qualified service shop that has Automotive Technicians.
As for the other member and the mechanical part problem , thinking about this a little and I am sure other Techs would agree he would have gotten other DTC. But I am not going to debate that.

 

I am very mechanically inclined. What would a scanner tell them at a dealer that is different than what my scanner tells me?