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Discussion Starter #1
Hello everyone
I have a strange symptom on my mazda3. 2008 , 2.0 L auto.

I feel vibration at idle in drive mode. For example stopped at red light.

Following jobs done recently.
1. I changed drive and AC belt
2. Flush the coolant system
3. Flush the ATF
4. I even put new transmission mount. After i felt vibration.
5. Replaced new spark plugs
6. Cleaned throttle body and Air intake filter.
7. Rotated my tires.

I checked passenger side mount , which is hydrolic, but looks good. I chaged it approximately two three years ago.

There is a rear engine mount, I bought new one but when I removed old one it looked good so I did not change it.
it is still origional.
What could cause such vibrations?
I need an expert opinion.


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Discussion Starter #2
Update :
I went ahead and put the new rear engine mount in. It seem to have reduce vibrations but they are still coming. :(
Am I looking at valve clearance check?
Or
Is it possible to have these vibrations due to brand new drive and AC belts?

any reply would be appreciated.
Thanks in advance.

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I had pretty major vibrations last year too. It was due to my 3 mounts being blown (Front passenger, Rear, and Transmission)
I'd replace all your motor mounts, not just one. They tend to go bad pretty fast.
 

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Discussion Starter #5
I had pretty major vibrations last year too. It was due to my 3 mounts being blown (Front passenger, Rear, and Transmission)
I'd replace all your motor mounts, not just one. They tend to go bad pretty fast.
Sorry for late update.
I replaced all three motor mounts. Car still has very fine vibration. I noticed that the RPM is very low while the car stopped at red light.
Now, Seems like idealing issue to me.

Please advise.
Thanks.
 

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Vacuum leak would be a possibility. The PCV hose under the intake manifold is usually the culprit.
 

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Discussion Starter #9
Vacuum leak would be a possibility. The PCV hose under the intake manifold is usually the culprit.
How can I diagnose this? Please help, I am still dealing with these fine vibration,,
I cleaned throttle body one more time, again, the throttle body looks pretty clean. Followed by I followed "RE Learning procedure" by keeping the car running for 20 to 30 mins hoping that computer will learn the normal ideling , Still No luck.

Please help, Thanks, in advance.
 

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Some things to check

Idle speed specification for 2.0 auto is 650 to 750 in park. If you have a vacuum leak, it can usually be found by spraying brake cleaner(with the straw on the nozzle for accurate spraying) around the intake and t/body and vacuum hoses to see if there is a rpm increase or stumbling indicating a vacuum leak as the brake cleaner introduces a burnable fluid through an unmetered air source. If you notice this in a area you can then narrow it down to see if it is a hose or a gasket or something. Sometimes the purge valve will stay stuck open causing a vacuum leak through the evap system. Usually you will get evap or lean codes in this case.

Normally a engine that has a vacuum leak for some time will set a check engine light with a fault code P0171- "Fuel system lean- bank 1". If it has a leak and doesn't set a code then you can usually see it by hooking up a code reader that has a data option and watching the long and short fuel trims. If you have a vacuum leak it will show high positive fuel trim percentages at idle that will go to normal as the engine is revved up to a off idle speed.

If it is not caused by a driveability problem then it could possibly be the mounts and/or installation of them. One way to tell if it is the mounts is to have someone take a pry bar and pry on the engine and rear mounts to see if the vibration changes. If it does then it is a mount issue. Also, there is a order of installation for them to ensure that there is no vibration after installation. The mounts are supposed to be tightened in a specific order with each bolt at each mount tightened in a specific order. I attached thumbnails in the order of when and how they are to be tightened. You should loosen the bolts at all three mounts and then follow the thumbnails in order paying attention to the tightening sequence. Trans mount followed by rear mount followed by engine mount. If your mounts are indeed good and you tighten them accordingly and you still have a vibration, then you pretty much can rule the mounts out.

This is a lot of information but should help in checking mount and vacuum leak causes. If these are good then you can remove the drive belts and see if it goes away which would indicate a belt or accessory issue(run it long enough to check but remember that the water pump is not circulating coolant and it will eventually overheat). Another thing that could cause idle vibrations in gear is exhaust hanger/ binding issues which can result from broken hangers or bent exhaust issues from hitting something or backing into something that contacts the tailpipe and bends things.

I'm sure if i think about it more things will pop up in my mind. These four things I've seen over the years that have caused idle vibration complaints.
 

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Hi I just purchased a 2008 Mazda 3 and I am having the same issue!!!! Not sure what the issue is but I'm bringing it back to my dealer to get it checked out. It started this morning when i was breaking at a light and I thought nothing of it until i had to go back out a few hours later then my car was shaking just when it was parked. I opened up the hood and noticed my engine was shaking crazily ): I hope this isn't a big issue because I've had this car for less than a week.
 

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Discussion Starter #13
I no longer own the car but mazda has that hydrolic mount where radiator reservoir hooked up. It leaks it's fluid and causes the issue. Very easy to fix except factory mount is expensive.

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