January 5, 2005

9:29 PM

I have a 1998 Honda Accord automatic sedan. When I am driving, it's pretty much fine...but when I stop at a traffic light or stop sign, the car starts to shake. When I start moving again, the shaking stops. If I am stopped (and the car is shaking) and I put the car in neutral or park, the shaking goes away considerably. Why does this happen? The one search result from Google that I thought would be useful points to a dead page. So I thought I would ask here. I just want an idea of what this could be so I can do some research before taking it to a mechanic and pretend that I know something about cars. And then maybe he won't try to trick me into getting things fixed that I don't really need to worry about. Thank you!
posted by omair to (15 comments total)

Could be a loose motor mount.
posted by kindall at 9:35 PM on January 5, 2005

Any other noise besides the shaking? If you take it out of gear (put it in park), and then put it back in gear does the shaking resume?
posted by pjern at 9:40 PM on January 5, 2005

No, no other noise. Just the car shaking (I feel the vibrations both in the seat and the steering wheel) and yes, the shaking resumes if I put it back into gear.
posted by omair at 9:43 PM on January 5, 2005

I second the motor/transaxle mount theory. If you're at all mechanical and have some jack stands, it might not be to bad to replace yourself.
posted by Doohickie at 9:54 PM on January 5, 2005

This page pertains to a 2005 Accord, but says the following which might apply to you: "The bulletin recommends replacing the motor mounts and radiator mounts in Accords that develop the idle-vibration problem."
posted by LeiaS at 9:55 PM on January 5, 2005

My '83 Accord had the same problem. I was told that it could have been transmission related, but I never worried too much about it because the car ran well in all other respects (and because I couldn't afford to fix anything non-vital on a student's budget). Whether it actually was the transmission or not, I don't know.

A quick Google search suggests that this is a common problem with automatic Accords. Given that, and given my own experience taking an Accord to various mechanics, I'd suggest you try to find a mechanic who specializes in Hondas. They'll probably have run across it before. Replacing the motor and/or radiator mounts is one oft-mentioned solution, but I've also seen people pointing to the transmission, a plugged exhaust gas recycling valve, etc.
posted by Aster at 10:46 PM on January 5, 2005

I'll third the motor mount suggestion. The other thing that can sometimes be a culprit is idle dropping too low while in gear. If you've got a tachometer, you can keep an eye on that and see if it's dipping into the sub 750 rpm range.
posted by icey at 11:06 PM on January 5, 2005

Motor-mount problems might go away when you accelerate or otherwise change the frequency (i.e., RPMs) or add/remove load, so that sounds plausible to me. See Icey's suggestion for diagnostics. I'm not sure if you'd be able to tell anything by looking at the motor mounts from any angle you can get to, but it's worth trying if you want to try to dope it out more before seeing a mechanic.

You could always try to get on Car Talk...

Devil's Adv: Also could be missing on one cylinder. Is there any smoking? Any difficulty in starting?
posted by lodurr at 5:43 AM on January 6, 2005

If it's not a motor mount problem, it could be a transmission problem. Does the car whine at speed?

If you can afford to have it looked at, don't delay.
posted by trharlan at 7:16 AM on January 6, 2005

Could try changing the ATF also. But it does sound like a "too-low idle" problem.
posted by knave at 8:22 AM on January 6, 2005

My first thought was that the automatic transmission might not be relaxing completely when the car is in gear & at rest. There's a thing called a torque-converter that basically takes the place of a clutch in a manual transmission. I think if your idle speed is actually too high, it could begin to engage the torque converter and cause vibration as the engine starts to pull a bit against your foot on the brake. Especially if your engine mounts are not the greatest.
posted by Tubes at 12:24 PM on January 6, 2005

Whether it actually was the transmission or not, I don't know.

People probably speculated transmission because this is a classic symptom of a sticking torque converter lock up actuator on GM FWD stuff. Usually though the car evenutally will stall every time you come to a stop.

You can get an idea of the condition of your mounts by have someone put the car in and out of gear and reving the engine a bit while you look to see how much everything is moving. The engine should move a bit but not be jumping all around. Sorry I don't have a more precise metric.

I don't have much Honda experience but many motor mounts can be changed with nothing more high tech than a jack and a couple closed end wrenches. Top "dogbone" style mounts are especially easy and often take the brunt of the torque load. Mounts are pretty cheap (on old american stuff anyways). I can change a 383 motor mount in my '66 in about 15 minutes and C$30.
posted by Mitheral at 2:55 PM on January 6, 2005

Not sure of your vehicle exactly however: If its fuel injected (as I assume it is) the idle speed will be controlled by a small valve that bleeds air past the throttle butterfly. The valve is controlled by the ECU (Engine Control Unit) - fuel injection computer. The valve usually receives a pulse width modulated signal to keep the idle constant regardless of engine load e.g. in gear, airconditioning on, power steering input etc. There is usually some mechanical adjustment for the datum of the valve (**only move this as a last resort**), chances are you may just have carbon built up on the pintle/orifice of the valve. If you're in neutral and you put the A/C on does it maintain a similar idle?, if you move the steering wheel, does the motor maintain idle regardless of power steering?
*of course, could be just engine mounts...*
posted by fullysic at 4:59 PM on January 6, 2005

Mitheral- You're absolutely right about the relative ease of motor mount replacement. I'm not proud of it* but I used to have a Ford Tempo. It had an oil leak right over the transmission mount. The first replacement took a couple hours, but I literally got to the point where I chould change it out in 20 minutes. (Oil can degrade the vibration-absorbing rubber in a motor mount.)


*Of course, I'm not any prouder now, since I'm driving a Ford Aspire
posted by Doohickie at 10:02 PM on January 6, 2005

I heard Ford had to rename the Aspire in English-speaking countries, as it reminded people of angry snakes...
posted by kindall at 10:33 PM on January 24, 2005