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Discussion Starter · #1 ·
Hey all- just made a fresh account on here because I’m doing my best to fix my girlfriend’s car! I’m typically an old school ford guy (1987 mustang 5.0!) so im trying to wrap my head around things.

So, it’s a 2008 Mazda3 with the 2.0 and an auto transmission
Symptoms- no codes whatsoever, though there was an exhaust leak that threw a code prior but no longer does anymore. This drives me crazy because given how the car acts i think it should definitely be throwing a code.

Car will drive almost perfect, especially on startup, but after a short time driving, the car spits, sputters, shifts weird, has next to no power (foot to the floor, shifts around and hardly accelerates, struggles to even make it to 40 MPH)

I’ve noticed that it appears to happen after going about 60 and cruising a while, then once you come to a stop and attempt to get back until to speed it just can’t pull itself together at all.

The engine noise noticeably changes and develops a loud hiss that isn’t present when the car drives okay. Sometimes it clears up for a short while but it typically returns. If i give it full throttle and let off it sometimes makes a bad blow off valve sound (mind you, this car has no turbo)
This hiss is also not noticeable at idle, only when driving, so i cannot hop out and try and locate the sound :(

what I’ve checked: removed coils while idling and all cylinders bogged down, so i know it’s firing right, i also listened to each injector with a screwdriver and I hear them firing as well.
I also checked the purge solenoid valve for proper operation and it works perfectly
Cleaned MAF and this helped idle but not the problem. checked air filter, looks good.

This feels to me like some valve that kicks open/closed and gets stuck open or closed once it goes into open loop or something. Could this be PCV? Intake shutter valve? Tumble shutter valve actuator? This has me stumped. Please advise!
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Discussion Starter · #2 ·
Turned out to be a clogged catalytic converter. Weird as hell that it didn’t show codes but it did when i removed o2 sensor and the car ran much better since it could exhale a little
 
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