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Slightly rough idle - shop not sure what's wrong.

1319 Views 8 Replies 4 Participants Last post by  tanbark813
My 2004 Mazda 3 has about 37,000 miles on it. I had to get an O2 sensor replaced at around 7,000 miles but since then it's been fine up until a week ago.

For the past week or so it's been idling rough. It's nothing bad that totally shakes the car, but it's definitely noticeable. It doesn't really happen when the engine is cold, only once it warms up. I took it in to Precision Tune Auto Care for a 30,000 mile service last weekend since I hadn't done that yet and I figured it might help. It didn't. The mechanic said that everything checks out aside from it running a bit lean but he doesn't know what's causing the rough idle or what's causing the mix to be lean. I told him about having the O2 sensor replaced but he said he checked that and that wasn't it.

I guess I'll just take it into the dealer and see what they say but does anyone have any other idea regarding what might be wrong?
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Go to the dealer and mention the top motor mount, they have a tendency to blow out and you'll feel vibrations at startup and at idle. This may not be the cause but its worth the shot. Alot of members here have had the issue and the mount was at fault.

Good luck.
I have the same problem. I know it, the dealer knows it - Motor Mount Number 3. There is a TSB on it. They should replace it under warranty.
They will, I'm on my 2nd.
Ok, thanks guys. I'll take it into the dealer and verify if that's the issue.
Bad gas possibly?
[quote author=SiXX link=topic=73125.msg1296852#msg1296852 date=1175103267]
Bad gas possibly?

The guy at Precision Tune suggested that but I gas up at the same place almost every time and this just started happening recently so I don't think that's it. And I always use 87.
let us know what the cause is, it could be a faulty injector, or a misfiring, etc....the cause could be something small.
*** update ***

Okay so I finally got it into the shop because I'm lazy. :D I took it into the dealer Monday morning and the tech called up in the afternoon and said he couldn't find any problems with it. I mentioned the motor mount idea but he said they're fine. He said they even tried to get the check engine light to come on but it all checked out fine.

I asked if he could recommend another shop that might be able to diagnose the problem but he got kind of huffy and replied with something like, "Well they won't have genuine Mazda computers to diagnose the problem and blah blah blah..."

The thing that kind of worries me is I'll no longer be covered under warranty in another 9,000 miles so I'm wondering if they're being shady and just holding off on telling me the problem--or letting it turn into something else--so they can make some money.
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