Rough running engine -- need help!
 

Hey, board. I've got a 2006 Mazda 3 (2.3L automatic) that I've been very happy with for 85k miles. I was hoping to hold on to it at least another 2 years, but now the engine is running rough and I'm not sure what to do. So here I am asking the board!

When I'm accelerating the engine starts to vibrate more than I'd like around 35-40 mph and then goes back to normal. The vibration doesn't seem to happen at shift time and doesn't seem to happen at a certain rpm. It just happens at a certain speed, and only while accelerating.

Some more history: one of the (I believe 3) engine mounts collapsed a few years ago, but the tech said it wasn't a real problem -- it just meant more noise, so I left it.

Then a few months back, my CEL came on and I had to have the thermostat in the engine replaced. The extra vibration started around the same time, so I'm trying to figure out if the combination of the two explains the vibration.

So, could a collapsed engine mount cause the extra vibration at a certain speed?

And would replacing the thermostat move the engine around enough to make it worse?

Should I repair the engine mount anyway? (~$150 I think)

And, most of all, does this sound like something dangerous?


Thanks, everyone. I really appreciate any advice.


Astor

engine mount was my first thought, i'd heard of others complaining of vibration, and the engine mount (upper on the passenger side) was the fix.
As for when the vibration started, the tech that replaced stuff could have bumped something, or forgot to tighten something. Maybe even a wheel weight got bumped off - see if you have any 'clean' marks. Though that won't usually happen at 35-40MPH it's a possibility.

I doubt it's dangerous, but... is the vibration in the steering or anything? how can you tell it's just the engine?

Thanks for the response, djs2571. I can definitely feel the vibration in the steering wheel, but even the passenger notices it. But the only thing really pointing to the engine as the cause is that I knew a mount was busted.

But last week I took my 3 in to have the tires rotated, and went ahead and had them rebalanced as well. A vibration still kicks in around 40 mph, but it is much reduced. So at least part of my problem was the tire balance.

I suspect the remaining problem is just the engine mount, and both you and the tech that pointed it out agree that that isn't dangerous, so I suppose I'll just let it rest.

thanks,
Astor

rotate the tires one at a time to see if one is still out of balance. shops don't seem to balance as well as they can on the first try, i've been frusterated with multiple places having to balance tires multiple times to get it right.

Multiple rebalances? I'll give it a shot. At least it's cheap!

thanks,
Astor

Also if u have a tire that has a separated ply, it'll do the same thing. U'll know by an egg shaped bulge in the sidewall(usually on the inner sidewall) or even in the tread. Hope u find the problem.

The tires are fairly new (7k miles) and I've now had them rebalanced twice and neither tech thought they had a ply separation problem. I sure don't see a problem myself.

But unfortunately the vibration is getting worse, so I took it in to Pep Boys today. They think it's a transmission problem (which they don't work on), so I'll be looking around at transmission shops and trying to decide how much money I want to put into this.

Thanks for the well-wishes.

Astor

did you try swapping tires around to see if the vibration follows? that would be easier than the trans shop as a first shot at finding the root cause.

Yes, I rotated the tires once and rebalanced the tires twice. But the problem persists.

On the advice of a friend I checked the transmission fluid and it looks fine. So I guess I'll have to take it to a transmission shop.

Hey board, I have 2004 mazda 3 2.3. My engine is running rough at idle and I cant gas it or anything for the most part. My check engine light is on. I've already changed all 4 coilpacks and spark plugs. I cant drive it to autozone to get the code read. Can someone help me. Oh a side note I have 135000 miles on it 1 owner (me) and it is a manual trans.