P0300 - code any ideas

smetzger

03 P5 (x2), 09 Miata, 07 Mazda3, 13 Fit, 09 Ody
I am getting a P0300 code random - multiple misfire

There was oil in the spark plugs so I replaced the valve cover gasket, plugs, and wires (timing belt looked good).
Started up fine afterwards.
Let it sit overnight, then started it up and engine idles very rough and CEL starts blinking.

Any ideas what could be causing this?
 
I had already replaced the hose between the air intake and the throttle body (previous owner had it duct taped up).

Just replaced the PCV, and one coil pack. I guess if it still pulls a CEL I'll switch the new one to the other side.

I had previously pulled a P0421, and have replaced the lower Oxygen Sensor. I still haven't run the car enough to see if that's fixed.
So I suppose it could still be the Cat.
 
Did the coil pack change work? I had one that didn't work and to diagnose it I pulled the wire on one, started it - same performance. Pulled the other wire - no start. That was the coil I replaced and she's working great. (P0300 code.)
 
Shop only had one coil pack. I replaced the left side (just a guess since it was running fine at the time).

Had a rough start and CEL yesterday, pulled the cable out of the older coil pack and it still idled roughly. Pulled codes and got a P0300 again.
So I put the coil pack that I had taken off and put it on the right side.

So, _this_ code hasn't come back. But I don't think I had done enough starts to know (previously I had gotten the code only on the occasional startup).

Ran through the drive cycle (http://www.mazdas247.com/forum/showthread.php?123759295-Found-a-successful-Drive-Cycle-formula!)
this morning, CEL cam on and I am now getting a P0171 System too lean (Bank 1).
Despite running through the drive cycle my scanner is still showing that the CAT, O2, and EGR have not run through their tests.

I'll clean the MAF and check the EGR valve tonight (several forum posts seem to indicate these are the usual suspects)

I didn't clear the code yet. I'd like to figure out if I have fixed the P0421.
If I just keep driving it without clearing the codes, will it continue to check CAT, 02, and EGR? and hopefully I get a more complete list of codes?
 
I cleaned the MAF last night, but I did NOT check out the EGR valve.

Ran through the drive cycle and the CEL went off.

Scanned the codes and it is still showing a P0171, with CAT, 02, and EGR not ready.

So... why did the CEL go off if I still have a code? How the heck do I get the CAT, 02 and EGR to be tested?
 
Cool link to the drive cycle; I'm gonna try that tomorrow. I have a P0140 come up after changing the O2 sensors, so I think I will clean my EGR and then do the drive cycle . The info I got from youtube and Autozone was to clean the EGR (MAF cleaner works) to see if it would clear the problem. It is set off from my second sensor, so I am not quite sure if that would really affect it. I don't know how to get that tested yet - but youtube and this site has been a savior for me. Thanks again for the drive cycle link.
 
I am thinking of doing a seafoam. Anyone know the best place to suck it in and do it?
 
If you have a blinking engine light, its a critical problem...its actively missing (a solid light can occur from just a few cycles), which means its just pouring raw fuel into your exhaust system...if you try to drive it like that, you'll quickly burn up the catalyst comb's...and literally weld it shut...

an active miss such as this narrows it down almost always to ignition...and my guess is its the 'other' coil pack (you said only one was replaced, right?)...those have a recommended service life of about 100k, but most of us manage 125k or 150k miles...either way, if there is any doubt, make sure both are new or as close as possible...

just saying...an EGR under no circumstances will get it blink...you'll pop a code every once and a while, might get a rough idle and the occasional stall...but it won't cause constant missing...

another possibility is much less friendly...check your plugs again...are you getting a lot of white smoke on cold starts?...cold start smoking is usually valve seals leaking...no smoke on start up, but still getting fouled plugs is oil rings being clogged, and/or compression rings failing...a proper compression or leak down test will let you know what kind of shape the cylinder walls are in, and you can rent the equipment for free from Autozone...
 
Yeah, P0300 is gone and hasn't come back in awhile. I'm gonna call that one fixed.

CEL is off, but scanned the codes and it is still showing a P0171, with CAT, 02, and EGR not ready.
It is NOT a pending, the P0171 was showing before I cleaned the MAF. I cleaned the MAF and did not clear the codes. CEL went off by itself.

I have almost 100 miles since last clearing of codes. Why is the CAT, 02, and EGR not ready?
 
Ok all fixed.

Here are the codes I was getting and the fixes...

P0421
- replace 2nd/lower O2 sensor

P0300
- oil in spark plugs - replaced valve cover gasket, spark plugs and cables
- coil pack bad - replaced

P0171
- vacuum leak on the PCV valve - put a hose clamp on it
- replaced first/pre-cat/top O2 sensor

P0140 - Pending only
- replaced first/pre-cat/top O2 sensor

One thing I did notice is that the CAT/O2 sensor would not be tested even after several drive cycles and 200 miles of day-to-day driving. But, as soon as I replace that top O2 sensor they were tested in one drive cycle. So, if your trouble shooting something and you have replace something and cleared the codes but its not going to tested/ready after a couple of drive cycles then your probably have not fixed the problem.
 
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