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Hello all, I'm completely stumped on a major issue my car has been giving me. Really hoping someone here can give me some advice.
I've had my automatic 2004 Mazda 3s hatch for just over 6 months. It had About 100k when i bought it, has around 107k now.

About a week ago while driving i noticed a massive loss of power in 3rd and 4th gear. As well as the car surging starting at just under 40mph, every time. On top of the surging the rpm will also rev up to 3k+ and back down but I'm not actually going any faster.

Going uphill all of these problems are magnified, i basically have to make it uphill on momentum or use the manual shift to drop it into third. In 4th going uphill the rpm will just jump and sometimes i will get a rumbling from under the car.

Initially i thought my catalytic converter was jammed up. The only CEL codes i had when i bought the car was p0420. It stated i had a problem with the precat, as soon as this problem started i gutted the pre cat and checked out the main cats, the main ones looked clean and clear so i left them alone. This obviously didn't fix the issue. The next thing i did was change the transmission fluid and filter. The fluid came out black but there didn't seem to be many shavings in the pan. The day i changed the fluid and filter i was test driving to see if it helped when i got my first AT light on the dash and the car wouldn't shift at all. I pulled over immediately and noticed some fluid leaking. Got back in the car started it back up AT light is gone car drives with the same original symptoms but gets me back home. Ran codes again and got p0751 - shift solenoid a stuck off. I checked the fluid and it was low again which makes sense considering the leak post change. A symptom of that CEL code is low trans fluid so I'm thinking this code is a direct correlation to me changing the fluid and not my original problem. But I'm not sure.

So that's where i am, lost and not sure which direction to go now. I fear a transmission problem but i wonder why no CEL, code or AT light the whole time I've had this issue if that was the case?

Sorry this is so long, but i wanted to give as much information as possible. This has got me in a tight spot and i really don't know how to proceed. Transmission? TCM? Solenoid? Torque converter? Main cat? Something else? Hoping someone knows. Thanks guys.
 

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Demon Spawn
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honestly it sounds like a transmission control module failing or the shift solenoids for 3rd and 4th are gummed up. your changing of the fluid was probably the first time it was ever even touched as most people ignore the auto tranny and its fluid until it becomes a need this fixed now type issue. at 100k miles if it was the first time the fluid had ever been changed it may also be missing a bunch of material off the clutches and this is causing the gears not to engage as they normally would making the car freak out and thus surge like you are seeing as it tries to go into gear but cant. without knowing the maintenance history of the car or being able to look at it in person its hard to say 100% what your issue is, if it where my car i would find a trusted local transmission shop and have them do a diagnosis (usually charge for this but its cheaper than throwing parts and time at it and you will more than likely know exactly the issue and its fix) and let us know what they say
 

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Discussion Starter #3
Hi, thank you so much for the fast reply. Despite the symptoms not perfectly matching they were close enough that i had suspected the TCM. From what i understand a damaged TCM can often be visible as they seem to burn up. It looks easy enough to get to so i was going to have a look at it today. But is the tcm unmonitered? Wouldn't it throw a code? Thanks again, appreciate you.
 

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Demon Spawn
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yea i gotta agree with kms1990 on this issue. If the fluid was "black" as you say its most likely burned deep red and stank like hell meaning serious overheating of tranny at some point, either that or someone put something other than trans fluid when they last filled it. Either way a quick rip to a tranny shop, if you can make it, is the prudent thing to do.
 
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