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Car Vibration In Drive While Stopped


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#1
pingu

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I have a 97 626 Automatic 4 cyl. Why does the car vibrate when I'm stopped at a stop light and the transmission is in "Drive"? The vibrations goes away when I put the transmission in neutral or park. I'm trying to figure out whether or not the problem is due to cracked engine mounts. I see a crack on the passenger side top mount, but I can't see whether there's any cracks in the rear firewall mount and driver side top mount (near the battery).

I have read some posts from people with similar problems and suggested solutions.

Some posts say the problem is bad idle. My idle speed in park or neutral isn't noticeably less than the idle speed in drive. I revved the engine up to 1000 rpm in park/neutral and the car did not exhibit more vibrations. So I don't think it's idle speed related.

I've also connected a vacuum gauge to the PCV valve vacuum hose and didn't see anything abnormal. The needle was steady. Perhaps I should repeat the vacuum test and put the car in drive with the brakes applied?

So I suspect the engine mounts are the culprits, but the rear one and driver side top one is hard to inspect and to take out. If I just replace the top passenger side one, I'm not sure if that will help or not.

#2
tradosaurus

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I would get in the habit of putting it in neutral when stopped at lights. Posted Image

I'm not sure but your gas mileage may get better and your car runs smoother in neutral, at least mine does.
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Of course check your engine mounts but if those are OK and I wouldn't worry about it. Posted Image

#3
Mazda 4 life

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The mounts are definitely the problem. This is a tough job to do on your own I would suggest taking the car to a stealer and having all of the mounts replaced because the failure of one puts more stress on the remaining mounts. My rear firewall mount failed causing the rest of them to ware it cost me $1400 to replace all of them. It definitely helped.

#4
DirtyErnie

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just because your idle speed in drive isn't appreciably less than in park or neutral doesn't mean that you're safe from vibration. There's some kind of harmonic mode (I notice it on my car, too) just below neutral idle that puts the engine at the right frequency to vibrate, and the added power requirement of turning the transmission when stopped in drive increases the amplitude of the vibration, meaning you feel the whole car shake. More than likely it's no big problem, just stick it in neutral like the other guy says and it goes away. if you can grab your engine and give it a good shake and it's flopping around, then you definately have problems, but if you don't hear any nasty klunking noises when you go into reverse or drive you're probably safe.

E

#5
MAL

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1997 Mazda 626 AT, I am having a similar issue. I have to put it in neutral at stop lights with brake on and it smoothes out. While I accelerate the roughness goes away. The one thing I do find strange is I bought the car a couple of months ago. It was rough then, but I from past experience it felt like a vacuum leak. No big deal, find the leak fix the problem.
Well I did find a hose going from what looks like a black cover down by the tranaxle, facing the front by the radiator. It is connected to the box cover by a clamp. From there the hose goes up onto the right side of the air cleaner case, where it has holders for it. It runs past the air filter and then the physical hose has a downward turn to it. This I have been told is a vent hose and leads to nowhere. What makes that hard to believe is you can visibly see where a clamp was in place at the end of the hose. I have looked all over the engine and compartment to see where this thing belongs.
I have cleaned the MAF, IAC, put on a new fuel filter. The person who I bought it from had work done on it and the following are new.
Dist. Cap and rotor
Spark Plug wires
PVC
So what I suggest is look around the compartment and see if anything is not connected or out of place. I would love to know what the black cover the hose is going into is. It might make my trouble shooting easier.




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