When it's at idle when AC is on the RPM's are 600 and engine has very noticeable vibration. If I press on the accelerator peddle and increase the RPM's to about 750 to 800 the vibration mostly goes away. If I turn the AC switch off the idle RPM's go to 750 - 800 with very little vibration. There is no vibration under any other conditions and the AC works just fine. I haven't attempted a repair yet. Can someone give me some ideas where to start looking for the problem?
1991 Honda Accord DX 4 Dr. Sedan, 5 speed Manual Transmission
125 horsepower (93 kW), 4-cylinder, 2.2 liter(F22A1)
16 valve electronic fuel injected engine (PGM-FI)
VIN: 1HG CB7 5 4 4 M A 170164
175,000 miles

 

your ac runs off the engine when you engage the compressor you put extra load on your motor causing the idle to drop making the engine shake its very common with smaller cars like honda's. this could also be caused by a dirty idle air control valve (IACV) you can remove it and clean the inside. this will explain everything
http://ecomodder.com/forum/showthrea...ained-967.html

 

Thanks lowlife9. This is great information and gives me just what I was looking for - a good place to start looking for the problem. I'll post back when I get a chance to make these checks. Its hotter than Hell here in PA right now so I'll be waiting until the weather cools a bit before working on it since its not an emergency andIcan drive it.

 

i hear you im in connecticut in the middle of a record breaking heat wave but good luck with that.

 

The problem your having with the strong vibration could also be (check these areas):
bad balancer pulley
bad engine mounts
bad accessory pulleys
check your timing on your distributor it could be off by a degree causing unsmooth idle (probably not the case)
dirty IACV
possibly a dirty PCV valve also

 

Thanks RiceCanRacing. I'll include those checks along with the other suggestions I've received.