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Rattling passenger front side, only while in drive and idling...

36K views 16 replies 5 participants last post by  Horea 
#1 ·
My car has been doing this for the longest time and it honestly hasn't bugged me enough but I decided to start getting these issues fixed as I'll be still (hopefully) driving this car for another 3-4 years (and it's almost at 100k) .

What happens is occasionally while in drive but idling (sitting at a stop light) it sounds like a compressor or something is clicking on and causing vibrations which is causing something to rattle... because the vibrations get louder, and then they stop when whatever was vibrating cuts off... if I shift it into neutral when it's sitting there, the vibrations stop and the rattle stops. It's not excessive vibrations, the idle would be fine if it wasn't for that rattle. Whatever sort of sounds like a compressor clicking on doesn't stop when I shift into neutral, but the vibrations stop which stops the rattle.

There is also what sounds like a metal on metal twang when you start the car, I thought it might have been the exhaust but I'm not sure. Another tech mentioned it could be the heatshield, but I honestly don't know where that is. It sounds like it's coming from the front passenger side. It doesn't seem to effect anything, but it's embarrassing to start the car because it sounds silly.

So I guess I'm wondering if anyone else has heard this before or has any ideas... thanks
 
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#2 ·
Well I found out that it was the compressor turning on, but the car still rattles, just not as bad with the compressor not running.

Apparently switching it to defrost turns on the compressor for the AC, but the AC light doesn't come on, so I didn't realize that the AC was running... that would explain my terrible gas mileage I've been getting for a while... 25-27mpg on highway when it should be closer to 30... I usually always set it to defrost because the air from defrost seemed to be more pleasant (which makes sense that the AC was de-humidifying it).

Either way... still have a rattle and that clang/twang on start-up... any ideas?
 
#4 ·
Looks/feels fine...

But here's what I figured out after a bit more with the car.

What happens is when the car is in drive and you step on the brakes, the RPM's drop a little bit and that's when it begins to rattle. When I looked in the engine bay itself (using a 2x4 to hold the brake down just incase, along with parking brake... ) the engine starts vibrating pretty bad, shift it into neutral and the vibrations stop and RPM's rise back up.

If I don't have the brake pedal depressed, but in drive / parking brake then the engine is identical to when it's in neutral, idles at the same RPM and doesn't vibrate.

I read somewhere that with the automatics, when you come to a stop it cuts off some of the fuel to the engine when you're braking to save some gas or something. I think that might be what's happening but I have no idea why it vibrates like that. You can barely hear the rattle from the engine bay though, only seems to be inside the car you hear something rattling. But it doesn't seem good that the entire engine is rattling/vibrating like that.

I could take a quick video if that would help

Doing more research this sounds like the "low idle while braking" and related to the throttle body being dirty... the car has about 96k on it and the engine is ~30 less then that. But I believe I had this issue with the original engine, and I don't know if that would have been swapped with the replacement anyways...
 
#5 ·
Decided to try Seafoaming the engine, it seems to run smoother but didn't help with the low idle / vibrating...

A lot of smoke poured out, took 2-3 minutes of driving at 30-40 mph before I didn't see any..

But still have an issue... may take the time to clean the throttle body myself in the next few days and see if that helps, or let a local place do it... they said $44 bucks...
 
#6 ·
Been reading more.. Mazda had a TSB out to clean the throttle body...

I've been putting up with this issue forever and finally decided now is the time to fix it.... Well cleaning the throttle body didn't help, but it was an interesting experience. Now I think the last thing to look at would be the passenger side motor mount, but when I've heard those go out it usually vibrates much worse and at different speeds... my car is perfect at any speed but idle w/ brakes on.

Throttle body was caked on with black crud, completely covered, and all the way down into the engine. But eventually I got it almost 100% clean... but didn't fix my roughish idle when you are in drive / w brakes... but it made it a bit smoother, but I also just seafoamed the engine and cleaned the MAF... Throttle body was last on the list of "fixes" because it seemed the most time consuming and I guess I was right... I've been annoyed by this long enough, so much so that I was outside taking the throttle body off with a flashlight at 3am. And usually I don't even do my own oil changes..

Luckily nothing went wrong and the car feels much better, pulls harder in every gear and is smooth throughout, no more random jerks from shifting (manual mode was worse than automatic, but now manual is perfect).

The first picture I had already started cleaning it (the silver spots) before it was completely black. Terrible pictures from my camera phone...




 
#7 ·
Damn, you're not going to let this one go huh? My 2004 has kind of a rough idle when stopped and on the brakes. I know my passenger motor mount is bad, but I haven't been able to replace it. My RPMs also fluctuate some too while I'm sitting and the idle gets worse at about 500 RPMs.
 
#9 ·
~ 5,000 ago at the 90k service I believe... I'm at 95600 something right now, need to get the oil changed soon.

It's been doing this for as long as I can remember... but the rpm's don't fluctuate. It drops slightly below the neutral idle and the car starts to vibrate. Only happens when you press on the brakes, but if you use the parking brake and put it in drive, it's like when you leave it in neutral. If I'm going to be at the light or whatever for a while I'll just shift into neutral to make the vibrations stop, but it seems like a lame fix. And there have been times when I forget to shift back into drive and start revving my engine like an idiot when the light turns green :shock: haha...

So right now I'm not sure, this was only ~$20-25 in buying some cleaning stuff in attempts to clean all these different parts, but cheaper than bringing it somewhere for them to tell me "well nothing is wrong lol!" because I have a feeling that's what most places would say. I've also not gotten a CEL in the longest time which I find odd... I can't remember the last time I had one...
 
#11 ·
I'm pretty certain, others said there would be fluid leaking and it would move a lot, it feels solid and no fluid leaking out.

Plus I've heard replacements aren't all that great if you buy OEM and haven't heard of any aftermarket that would be better.

It seems like there a lot of threads with this same issue, but some are worse than others.
 
#13 ·
If you got some more info on what to look for I can check, I felt around for any oil or rubber falling apart and it all felt solid / not greasey/oily.

Little dirty because I've never cleaned the engine bay it the entirety of owning this car... but still runs good :)
 
#14 ·
Put your car in drive or reverse and place the brake on. Try to see if the engine moves exessively when you accerate. If it does it its a mount. If it has that many miles on the car it is more than likely a mount. There is the passenger side mount, the firewall side by the oil pan and the other should be under the battery holder. I had to replace all three of mine and it increase performance and stability to the front end. I thought I only needed two mounts and come to find out the trans mount was competely shot.
 
#15 ·
I'm 90% sure it isn't the mount... I've looked at them, and watched the engine when it is rattling and the entire engine bay is rattling, as soon as you let off the brake it goes back to running smooth / no shaking or rattling. I could take a video later on.

It's that the idle drops down below an acceptable rpm and the engine starts running rough which is where the shaking / rattling comes from.

As long as the rpm's stay at or above 700 rpm then it doesn't idle rough and doesn't shake/rattle.

This issue only happens when you're in drive and foot on the brake. If the car is in drive / parking brake is on then it doesn't drop the idle and no rattle. Something to do with maybe the car trying to save on gas or similar by tuning the engine down when you're braking (which makes sense) but it might be too excessive...

This issue is less common after I've done this work, but it starts only after the car has warmed up. Immediately after starting the car you won't see the issue for a few minutes.

I might have to replace the CV Axle so I'll have them check the mounts and verify they're good.
 
#16 · (Edited)
rattle noise while in drive but stopped

I've been having the exact same problem. No point in describing it again as it is identical: ratlle noise when car is in drive but stopped at traffic lights for instance. Have been trying to figure it out for a couple of months now and I just won't quit. I have no idea what causes that rattle and is driving me nuts. Engine mount is OK though. I checked. The rattle occurs when the RPM drops at about 500 but the RPM dropping is absolutely normal when you put the car in drive. The RPMs always dropped with any car I've owned so that's normal. A manual's RPM would also drop if you put the car in gear and release the clutch a bit with your foot on the brakes, so nothing unusual there.

It would be greatly appreciated if anyone woul help out and post a follow up. I read Blazestorm's posts several times now. I wonder what did he do eventually to fix the rattle and what was causing it. Any pertinent help would be greatly appreciated.

Thanks!
 
#17 · (Edited)
OK, I figured it all out eventually. I read and re-read many many posts on the net about this issue. Several guys couldn't figure it out and took it to a dealer and had the timing chained replaced and flushed the transmition fluid and all that but I thought it couldn't have been that. Now of course, if you change the oil and timing chain and spark plugs, and fuel injectors, and air filter and what not, the car might run just a tiny bit smoother which means the rattle might be gone for a couple of weeks or so, but that's because the RPM won't drop quite that low. That's like treating the symptoms, not the cause.

Anyways...after about 3 months of trying to figure out what was causing the rattle - I had the brakes pressed down with a piece of wood set against the steering wheel and opened the hood and all that - but the thing is that you can't really hear the rattle once you get out of the car, I had to rely on someone else being in the car and me messing with different stuff under the hood. Bottom line is, I pressed and pulled different parts to see if the rattle would stop and at some point I pushed hard on the motor mount with a piece of wood and the rattle stopped. I previously thought it could't have been the motor mount as there was no fluid licking and it seemed solid, but it turned out that it was indeed the motor mount. The fluid probably licked out long before the rattle appeared so I didn't notice it. With the weight of the engine on the mount you can't really tell whether it's the mount or not, so stick one end of a long piece of wood between the motor mount bracket and the engine and push hard on the other hand - and I feel very confident the rattle will stop - if your symptoms are similar to those described in this thread.

Changing the motor mount is a 30 minute job. The mount was $85 here in Canada - I only purchased the mount and reused the bracket as it is a 2 piece thing and the bracket is nothing but a piece of metal. Before attempting to remove the motor mount with a 17mm socket, jack up the engine a few inches from underneath to take the weight of the engine off the mount. All you need is a 17mm socket and a jack for the engine. If the coolant reservoir is in the way, snap it out with your bare hands.

Remember, changing the air filter, timing chain, spark plugs and all that might make the rattle disappear but not because that was the problem, just because it makes the engine run smoother and at higher RPM and therefore vibrate less so you're not really fixing the problem, you're just covering it up and the rattle will reapear.

I hope taking the time to type these lines actually helps a few do-it-yourself guys out there. Cheers!

Maybe I shouldn't be doing this, but if you have questions, e-mail me at jimoniea@yahoo.ca and I'll see what I can do.
 
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