07 Mazda 6 - 4 cyl - my nemisis

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Chester11

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Hey folks:

I have posted before, but am taking one last shot here. I am chasing a vibration at idle, and have thrown a bunch of parts at the problem with no success.

I have replaced all 3 motor mounts, a brake line check valve, spark plugs, and even the brake light switch. I also cleaned the throttle body, and mass airflow sensor. (The brake line check value was replaced because brake reserve was lost when sitting overnight. The light switch was clicking loudly, and I was thinking it may be impacting the idle speed somehow).

Fuel trims at idle seem good (slightly positive) when the vibration happens. It is the worst when warm and the brake is on (say at a light).

The trans was rebuilt several years ago. (I started down the motor mount path because 2/3 attach to the trans. All three were worn, but not broken). The car has never idled smoothly, but has gotten worse since the trans rebuild.

Any other ideas I missed? The brakes work well, and the booster holds vacuum, so I ruled it out.
 
Have you looked at the Harmonic Balancer / Crank Pulley?

Is there a vibration only in gear?

Also hook up a vacuum gauge and idle it in gear when it's fully warmed up and see if the gauge flutters up/down instead of remaining steady with minor changes. A fluttering vacuum gauge indicates a mechanical problem or some sort of vacuum leak.
 
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Tank purge valve closing properly?

VVT on it? ......... questioning dephaser and timing chain/guides/tensioner mechanical condition ................. what's oil pressure doing when hot even though idiot light doesn't come on?

Post a video of the funky idle?
 
vibration is only in gear (drive more so than reverse). idle speed is pretty steady according to my scan tool. vacuum is steady in gear / warm.

I'm not sure if there is a PID for oil pressure - I'll have to look. I think it has VVT - there is a solenoid I think I unplugged during one of the procedures to see if it changed the idle speed.
 
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When you are in gear if you hold the break and give it a little throttle to increase the RPM as slightly as possible does the vibration get better? Also do you have a way to see the RPM's in gear and out of gear digitally so we can get exact numbers? Also how much do they fluctuate while idling (15 RPM or like 50 RPM)

Also what about the belt tensioner. My Santa Fe's belt tension went bad and it felt like the car had an engine shake until I changed it. (Just trying to give you other things to look at)
 
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slightly increasing RPM seems to improve the vibration (brake on).

I'll see if I can post some graphs from my scan tool. I would say about 15-20 RPM change.
 
If it's not idling too slow then I would check into the Harmonic Balancer / Crank Pulley or accessory belt tensioner (less likely) because the engine management systems seems to be working from what you describe and from what you have replaced already and if the vacuum gauge isn't fluctuating I don't think it's a mechanical problem. (Albeit this is internet diagnosis and all)

I know how frustrating this can be because I went through something similar with my Caravan trying to pin down what felt like a slight miss but turned out to be the coolant temperature sensor throwing off mixture just enough, literally a $10 part.
 
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2 of 3 are mazda parts. (I did the rear "dogbone" and trans mounts first).

The last one is from NAPA - I did it last week as a flyer to see if it made a difference. (Parts are getting a bit nutty for this model - long lead times and expensive).
 
Originally Posted by KrisZ
I'm pretty sure the 2.3 MZR motor has an internal balance shaft assembly and not a harmonic balancer integrated into the crank pulley.
Was the bottom end ever touched on this engine?

I googled it and it shows Harmonic Balancer pulley. And Rock Auto lists a Harmonic Balancer bolt and this type of crank pulley. I wouldn't have put it without checking first.
grin2.gif
 
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These engines are definitely internally balanced.

What did you use for engine mounts? They are VERY picky. Especially in an inline 4. OE or bust for the one that attaches to the right fender.
 
Mine had developed small vibration after 180K at a traffic light; it turned out to be passenger mount, the one with the fluid; not much other I did to the car

also I'd look into your fuel injectors; you may look for quality gas place or even use premium gas for couple of times in your car
 
Originally Posted by KrisZ
I'm pretty sure the 2.3 MZR motor has an internal balance shaft assembly and not a harmonic balancer integrated into the crank pulley.
Was the bottom end ever touched on this engine?


I don't think so (I bought it used) - only significant work was transmission rebuild.
 
I'm assuming its a regular vibration and not a hit-and-miss vibration?

Honda CRVs, the previous gen, had a horrific idle vibe in certain vehicles, when the AC compressor was not running. The fix for this was one engine mount, radiator mounts, trunk lid door hardware and revised headrests. The lower idle when the A/C pump kicked out would cause the vehicle to resonate, and honda had to isolate prime "shakers" and items that responded to those parts and modify both.

The hardest part was figuring out the mode in which the vehicle would initiate that low idle so that it could be demonstrated to the dealer - I knew there was a TSB for it. The fix however was telling of how many factors the engineers have to look at for NVH. Radiator mounts? really?

Yes, their fix worked. I don't know how far down that list they had to go, but now when it hits low idle, you can tell its right at that resonant frequency but it does not mushroom into the cave-your-head-in and shake the dash needles, thing.

did you use oem engine mounts?

m
 
2 of 3 are OEM. Supposedly the transmission and rear engine mounts get wrecked if the trans has to come out. So I did those first.

The passenger side mount is from NAPA. None of the mounts were broken, just slightly worn.

Based on the wear on the mounts I think something else is causing the vibration.
 
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