When AC is turned on in idle it shakes pretty badly, but it's fine while driving. Is this just normal for a high mile car?

 

No this is not normal,you mite want to check the belts and the pulleys.
check the belts for tightness,worn,
check all pulleys make sure there on tight and check them for cracks around the face of the pulley

 

If idle is dropping below 600 rpm when AC comes on, then something is wrong w/ idle control system. Clean throttle bore, throttle plate (both sides), and IACV screen/valve movement. This is usual cause of low idle speed under load.

If idle speed stays around 800 rpm when AC comes on, but vibration increases, then front and rear motor mounts should be inspected carefully for damage. Front mount can be seen easily, and rear motor mount can be seen from pax side. Apply engine pulses 1500-2000 rpm w/ ebrake and foot brake held tightly by trusted partner while you observe rear motor mount. In R, the mount should lift and damage will be evident.

good luck

 

It does drop. Would there be a DIY form on that? Thanks a ton.
Edit: I found some help in the manual on how to do it, but it isn't as detailed as I'd like.

 

I wrote a post about setting the "BASE idle" in the DIY section. Check that out.

HOWEVER...
For 1991 you have a boost-valve on the opposite end of the intake manifold. That is involved in the idle-control system and I don't have any experience with that. Not sure how that boost-valve changes things.

But it's tempting to adjust idle up or down without properly setting the base idle. That means jumpering the SCS connector and unplugging the IAC-valve. The system can operate with the IAC-valve at the wrong end of it's operating range but when the AC load is added it falls on it's face.

 

See following DIY link :

https://www.hondaaccordforum.com/for...leaning-36812/

I would first clean and see how idle responds. If still low, then a re-setting of base idle is indicated.

good luck

 

.....please check what the others have suggested, I'll only ask that you check the tune up items (cap, rotor, plugs) as soon as you can, sounds like you just got the car and may not know when they were last changed.

 

I changed the plugs recently and I know the cap and rotor were changed by the previous owner not too long ago. I bought it from a friend who is a mechanic, so it was kept up.