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Old 07-09-2010, 02:28 AM   #1
blazestorm
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Default Rattling passenger front side, only while in drive and idling...

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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Old 07-10-2010, 05:23 PM   #2
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Default Re: Rattling passenger front side, only while in drive and idling...

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?
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Old 07-10-2010, 07:09 PM   #3
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Default Re: Rattling passenger front side, only while in drive and idling...

Passenger motor mount?
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Old 07-10-2010, 07:35 PM   #4
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Default Re: Rattling passenger front side, only while in drive and idling...

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...
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Old 07-10-2010, 10:17 PM   #5
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Default Re: Rattling passenger front side, only while in drive and idling...

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...
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Old 07-11-2010, 07:30 AM   #6
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Default Re: Rattling passenger front side, only while in drive and idling...

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...




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Old 07-11-2010, 10:53 AM   #7
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Default Re: Rattling passenger front side, only while in drive and idling...

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.
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Old 07-11-2010, 12:43 PM   #8
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Default Re: Rattling passenger front side, only while in drive and idling...

A rattling/vibration when the car's in Drive but stopped would suggest something with the torque converter. When was the last time you got the transmission fluid flushed?
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Old 07-11-2010, 03:00 PM   #9
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Default Re: Rattling passenger front side, only while in drive and idling...

~ 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...
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Old 07-11-2010, 03:58 PM   #10
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Default Re: Rattling passenger front side, only while in drive and idling...

And you're certain your passenger motor mount is OK? I'd try replacing it anyway, it's only an $80 part and even if yours hasn't failed yet, with 95k on the car it's likely to fail soon.
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