I just bought an 04 Mazda3 hatchback and I love it! However I've noticed that it idles a little hard when I'm at a stop sign, the steering wheel will shake a bit, and the engine kinda revs a little, its barely noticeable butI can tell its doing it. The car also shakes a little when i'm driving around town, almost as if something is out of balance. Should I be worried?

 

Well, yes, and no.Here's my take.
I also have an 04 since it was new. These engines do tend tobe a little on the rough side... not completely smooth.I have assumed that thisis because the engine has an internal counter-balance shaft assembly and that Mazda, not wanting to put too much drag on the engine, went as lightweight as they could when designing this part.It's probably as lightweight as they could make it to help eliminate unnecessary rotating mass within the drive train.
However, engine mount #3, the one locatedon theupper passenger side of the engine compartment is a hydraulic mount (essentially a rubber bag filled with light weight oil) that isknown to leak and go bad.
Also, since you indicate that you bought yours used, it is possible that the previous owner installed an aftermarket #1 mount, also called the torque mount which tend to be muchfirmer than the OEand will cause vibrations. That's the one under the transmission.

 

Also possible that the previous owner never had any of the available reflashes done for the ATX in that car. check with the dealer and see if there are any available for yor car and see if that helps.

 

I have an 04 HB as well and mine tends to do the same thing. My Mazda dealership was bought out by Mike Raisor Fancy Oil Recycling Device, and the last day that they were working on cars, I ended up getting my PCM updated for free instead of the $75 they charge everyone else. Only problem with that is I ended up getting a new battery and had to have it unhooked for over 10 seconds (obviously) and IIRC the PCM resets when it's unplugged over 10 seconds. Did I lose all my updates that were uploaded to the PCM?

 

No as they updated the software.You don"t lose your computer"s operating system just because you shut it down, or unplug it from powerdo you? Same thing here.

 

What exactly are the updates you guys are talking about? Does this need to be done every so often?

 

Updates in the software that controls the car... engine/drivetrain specifically. Like a WINDOWS upgrade or a "patch."
And no, the only time you should get the PCM reflashed is if there's been an update from Mazda. How would you know? Good question.
Mine was reflashed when I started having issues w/the MAF sensor and rough running in general.

 

I would just occasionally go up to the dealership and ask the tech's if there has been an update. About every month or so.

 

get your car checked. I should not be running rough at all.