Help identifying cause of random misfire

[Schwamm]

A few days ago my car randomly started running badly all of a sudden. It sputters and won't idle. I was actually pulling up to a stoplight and after pushing in the clutch it just died. When I start it, it runs really badly and sounds like it's misfiring.

I got two CELs: p0131 and p0300, one of which indicates a random misfire, and the other low voltage on the heated O2 sensor. I have gotten these errors twice in the past year, and fixed them by replacing the O2 sensor (first replacement lasted 5 months, and now I guess the second one is done after 4 months). However, previously it would idle and run rough but never just die. Now it's noticeably worse, and my third replacement O2 sensor didn't fix the problem. It still runs just as badly.

I have tried putting in different spark plugs, swapping out coil packs with a spare one, and checking that all the vacuum tubes are connected. I have also done a lot of work recently, but it should be unrelated (CV axles, brakes, tie rod ends).

Anyone else experienced this, or have any ideas? I appreciate any input!

 

[CHIQLES]

id be wondering why my 02s are dying. is there any way for you to get the cat checked out?

 

[Schwamm]

Thanks for the reply, I've been wondering that, I'm trying to figure it out right now. Not sure if there's a problem with the car or the knock-off replacements though. I'm about to buy a real Mazda sensor, but for now these knock-offs are free under warranty. My car has been burning some oil lately, so I'm wondering if that's gunking up the sensor. Still don't know why it's doing that.

How would the cat affect the O2 sensor? How could I check it? My knowledge of car maintenance is limited, so I don't quite see how one could affect the other... could you explain a little? Thanks!

 

[Kelon32]

If you have an exhaust leak at the manifold where it meets the head the car will throw that code. The car will read the air leaking into the exhaust as a lean condition and add fuel until it hits the max of about 20% then throw a code for low voltage of the sensor because it cannot get the vehicle to run rich even though it is and it cannot see it. Also coil packs on these cars seem to cause most of the misfires that I have seen. But if that leak is bad enough it "could" cause a misfire.

 

[Dr0]

just start the car and feel around (dont touch obviously...) the exhaust with your hand and feel for a puff of warm air (exhaust leak). if you can find anything or unsure if you found a leak or not, have a friend put their hand over the muffler and build the backpressure in the exhaust (this amplifies any leak) if you have no luck finding one, then take your car to a reputable private shop (never the dealer unless its a warranty issue) and ask them to scope out the 02 sensor, any decent tech will be able to spot a dead/lazy sensor rather quickly.

and ive never seen an 02 sensor make a car missfire, but ive seen weirder things happen... im pretty positive you have 2 seperate issues and it may just be a coincidence. dont be missled thought, check your plugs if their really white with ashy deposites you may be running really lean and in turn could cause a missfire, but i dont think this is the case. if you could tell use the freeze frame data for when the random miss code popped up it would be very easy to tell.

 

[Schwamm]

Thanks for the input, I'll definitely check for exhaust leaks. I know it's not uncommon for the manifold to crack in these cars. I've been told my car has an exhaust leak based on sounds it makes when it starts in cold weather. It's definitely not a coil pack or spark plugs, I have extras I've tried swapping in. Spark plugs do have some white on them, but they're only 15,000 miles old.

I tried starting the car after unplugging the new O2 sensor, and it ran much better (though not perfect, obviously, but not constantly misfiring. it would at least idle). I'm guessing this means my new O2 sensor is a dud? Should I just buy a real Mazda one, rather than the $34 rockauto knock-off that this is? I'm guessing I need to first get a new O2 sensor and then figure out why it's running lean/killing sensors using y'all's advice.

Thanks for the help!!

 

[Stiki]

i have a major exhaust leak at my manifold to block and im not throwing any codes, when i got those codes i reset the maf sensor and replaced coilpacks and it went away

 

[Schwamm]

So I pulled the exhaust manifold out with the turbo, and there is definite oil leakage around cylinders 1 and 4, so I'm guessing some of this oil is getting onto my O2 sensor further down. I bought a new exhaust manifold gasket, so that should fix the leak problem, but I still have to figure out why there is oil there to begin with.

After soem investigation, I found that there is oil residue in the intake side of the turbo, so I'm guessing the seals on the turbo are broken, and oil is leaking through the turbo and getting sucked in with the intake. Sound reasonable? Anyone else have this problem?