Over the past few months, my car has been misfiring at idle and under hard/moderate acceleration. It is more pronounced with the air/ac running.
It throws 2 codes on occasion, random/multiple misfire and cyl#6 misfire. I have already replaced the spark plugs on cyl#2,4,6 (the front bank) and swapped the coils between the same cylinders.
I buy gas at the same chain of stations, not the same physical location every time. So I don't *think* it's bad gas, although I haven't tried a higher grade to see if that makes a difference.
Next step is to do a compression test this weekend and clean the maf. Baring that fixing or eliminating possibilities, what's next? I could take it to mazda/ford or my trusted shop for an hour of diag to see what they come up with.
Car has 152k and leaks ~1qt of oil between oil changes. I keep on top of oil changes (3-4k) and topping the oil off.
Tl:dr,
Misfire at idle and moderate/heavy accel, more pronounced with the air/ac on. New plugs, swapped coils around with no effect. suggestions?
My wife's 2006 4 cylinder manual had similar symptoms.
We unplugged the 02 sensor and the issue went away. Cant remember which 02 sensor it was (the one before or after the cat) Bought a new one and installed it and never had the issue again.
If its an O2 sensor problem, unplugging the upstream sensor would be the diagnostic thing to do. The downstream is just a monitor to make sure the cats are working.
Also check the intake boot for rips. They often get dry rot and tear
Curtis beat me to the advice on intake boot between MAF and TB. Also, the PCV tube back near the firewall sometimes splits but that's a big unmetered air leak so usually manifests as much worse than just a P0300
Oh, hey... weren't those in the years of the EGR solenoid failures too?
Mazda went through about a decade of poopy solenoids. The solenoids tend to fail allowing EGR leaks when they shouldn't. EGR should be metering exhaust gas during cruise only , so if its getting EGR flow during acceleration or idle that could be the issue.
Those solenoids also have a tendency to degrade the plastic over the years. You'll likely find that the nipple for the vacuum line has turned into something that is about as strong as a Pringles potato chip. It was a big issue for Mazda in the mid to late 90s. Possibly as late as 04?
In reply to curtis73 :
Intake is aftermarket, all the tubing looks good.
Unplugging the o2 sensor exacerbated the rough idle issue.
In reply to AngryCorvair :
PCV is the upgraded one from the 06-08 and is less than 2 years old.
