First of all, just letting you know, I'm not a mechanic or an expert, but I tried this and worked for me.
So I figured I would share this with you since it's such a common Honda problem
and I couldn't find any answer on google.

This apply to 1991 Honda Accord DX 2.2L
also can apply to other vehicles and years.

Hope this will help and/or wok for you too.

Step#1.

With the Fan OFF
A/C OFF
With the engine on and no CHECK ENGINE LIGHT ON,
Make sure that you don't have no vacuum leaks,
if the RPM surges up and down and up...then fix that first.
Then move on to STEP #2

Step#2.

Check all your motor mounts. Make sure they are all still good
then move one to Step#3

Step#3.

Clean your throttle, intake valve and EGR.

Step#4

Start Your engine.
Check to see where your RPM needle is.
Shift it to DRIVE with your foot on the brake
to keep your car from moving and remember where the RPM needle is at.

Now with your left foot on the brake,
Press softly with your right foot on the gas pedal til the vibration ease up or goes away to about 700-800 RPM.
If you need to go more than 1000 RPM then most likely you might have other problems.
if not then continue to Step#5.

Step#5

Now pop open the hood.
It's time to adjust the throttle cable to where in your RPM to where there's no vibration.
You will need a 12mm ranch.
To the right of the cable, you will see a bracket with the throttle cable running through it and 2 nuts.
Unscrew the left nut a little bit and then tighten the right nut (facing hood front to back).
The goal here is to raise the IDLE/RPM to where the vibration goes away.( It might take couple attempts )

With each attempts, go back into the vehicle and see where the RPM needle is while in PARK and DRIVE.

Do NOT adjust your RPM/IDLE too high, if it goes 1000 or higher then it's way too high.
You want to set it to exactly to where your vibration went away.
Probably around 700-800.

Tighten the 2 nuts. Then go back into the vehicle and double check if it's where you want/need it.

As your vehicle gets older and used, the throttle cable gets stretched out, that's why the adjustment is needed.

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Good Luck !!!

Click link to see an example of where to adjust

https://www.facebook.com/hondaaccord...type=1&theater

 

I would not ever recommend using the throttle cable to adjust the idle.

Honda's idle-control systems can be pretty funny, including back to 1991. There's an idle-control air valve (IACV) controlled by the ECM. In order for the different parts of the system to NOT be fighting against each other & fighting against your new adjustment, your throttle plate really has to close completely. The cable is not nearly repeatable for that.

The proper adjustment is a little needle valve in a recessed hole above the bore of the throttle body. The procedure is in a post by me about setting the "BASE" idle rpm.
https://www.hondaaccordforum.com/for...e-speed-38734/

It's real important to do the adjustment with the IACV unplugged, no loads on the engine, and to adjust to the lower "BASE" idle of about 550rpm (for most years up through 2002).