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Discussion Starter · #1 ·
My Matrix is running great when it is cold and then right when it gets fully up to temperature it will drop RPMs and vibrate. It is more noticeable in gear (particularly Reverse) but does it in nuetral and park as well. Whenever the AC kicks on everything will bog down and then bounce back to fairly normal.

Runs great when cold and very smooth.

Has new Intake Manifold Gasket, IACV, Throttle Body Gasket, Injector Seals, Coil Packs, Spark Plugs, and o2 sensors.
 

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マズダスピード3
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Could be a bad motor mount or trans mount. You could try to jack the motor starting at the trans mount. When the vibrating occurs, the increased angle should take away most of the vibration. Alternatively, it could also be the tensioner pulley. Try hand cranking the tensioner pulley. You can also remove the belt and run the engine. Don't run the engine too long without the belt. Can cause damage to your motor.
 

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Discussion Starter · #3 ·
I jacked up the passenger side motor mount mount and noticed no difference. I will try to get to the other mounting points and see what happens... Come to think of it my belt tensioner makes a rough noise intermittently and once the car warms up I get a tiny bit of belt squeal when in gear... So I can just remove the belt and run it just long enough to put into gear and test it?
 

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マズダスピード3
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I jacked up the passenger side motor mount mount and noticed no difference. I will try to get to the other mounting points and see what happens... Come to think of it my belt tensioner makes a rough noise intermittently and once the car warms up I get a tiny bit of belt squeal when in gear... So I can just remove the belt and run it just long enough to put into gear and test it?
If you run too long without the belt, it will severely damage the motor. Just till it goes into gear. Or hand crank with belt on.
 

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Discussion Starter · #7 ·
If you run too long without the belt, it will severely damage the motor. Just till it goes into gear. Or hand crank with belt on.
Thanks for the reply 75aces.

It seems way too stiff to hand crank so I'll try running it without the belt to see what happens... Would it be safe to get it warmed up to the point it wanted to vibrate then remove the belt?
 

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Discussion Starter · #11 ·
OK I replaced the belt and belt tensioner.
The engine runs much smoother now that the tensioner shock isn't popping.

There is still a vibration though.
I've checked and tested motor mounts and it feels more like the engine itself is doing something... Fuel trims look excellent and it is getting great MPG.

Gets much much better with AC on.
 

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Discussion Starter · #17 ·
UPDATE!!!

Changed the front motor mount and it was indeed warn.
The change made no difference and maybe even made it a more rigid vibration.

When I jack up the engine around the passenger side motor mount it gets way worse.
The engine is running great and fuel trims stay right around 0% at all times.

When the AC is on it obviously idles up slightly and causes the vibration to diminish, but the once it gear if you turn the AC on/off the car will lurch. It may be normal since it is such a strain on the engine to run the AC.

Any ideas?
 

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I have the same vibration in drive. When coming to a stop the idle sometimes dips and slightly shudders but recovers. Oddly, I've noticed it only does it after (for instance) driving it for the first time in the day... then i stop at a convenience store, get back in and restart the car, put it in drive, and thats when it happens. Won't shudder or vibrate on the first drive of the day; Only after restart it happens. Even then it kind of sorts itself out and does it only 25% of the time (which is still too much and drives me nuts).

I've changed intake manifold gasket to the new orange one (helped a bit), cleaned MAF, changed PCV and the hose, cleaned throttle body, cleaned IACV, changed spark plugs, air filter, and replaced the fuel injector o-rings and grommets. I'm starting to think its a fuel filter issue (which is supposed to be a lifelong part), maybe the actual intake manifold (which is plastic) has an invisible crack (vacuum leak), or the injectors need to be replaced.

Seems like everyone has this issue but nobody has found the exact reason :/

Edit- no trouble codes have ever been thrown
 

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Discussion Starter · #19 ·
I have the same vibration in drive. When coming to a stop the idle sometimes dips and slightly shudders but recovers. Oddly, I've noticed it only does it after (for instance) driving it for the first time in the day... then i stop at a convenience store, get back in and restart the car, put it in drive, and thats when it happens. Won't shudder or vibrate on the first drive of the day; Only after restart it happens. Even then it kind of sorts itself out and does it only 25% of the time (which is still too much and drives me nuts).

I've changed intake manifold gasket to the new orange one (helped a bit), cleaned MAF, changed PCV and the hose, cleaned throttle body, cleaned IACV, changed spark plugs, changed battery and air filter, and replaced the fuel injector o-rings and grommets. I'm starting to think its a fuel filter issue (which is supposed to be a lifelong part), maybe the actual intake manifold (which is plastic) has an invisible crack (vacuum leak), or the injectors need to be replaced.

Seems like everyone has this issue but nobody has found the exact reason :/

Edit- no trouble codes have ever been thrown
I'm fixing to change the transmission mount this weekend.
At this point I am highly suspect of the VVT solenoid not closing all the way after it gets warm. It has all the correct symptoms of it including showing 9.0 ohms at 68 degrees when spec is 6.9 - 7.9 ohms.

I can see daylight through it and think maybe the internals are wearing out.
 

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I'm fixing to change the transmission mount this weekend.
At this point I am highly suspect of the VVT solenoid not closing all the way after it gets warm. It has all the correct symptoms of it including showing 9.0 ohms at 68 degrees when spec is 6.9 - 7.9 ohms.

I can see daylight through it and think maybe the internals are wearing out.

I've been keeping up with your progress and I'm definitely interested in seeing how it goes so that maybe, hopefully, this problem can get fixed. Keep us updated please! :smile:
 
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