1990 Accord, 2.2L, 4 Speed Automatic, 128K miles.
When engine reaches normaloperating temp (after 2 minutes of normal driving) engine acts as if ithas a miss. Under light acceleration,between 1500-2000 RPM, engine "shutters" or vibrates badly. It is worse at 1500 RPM and slowly gets better through 2000 RPM. Beyond 2000 RPM it is OK. Also, when cruising at approx.40 MPH (1800 RPM) vibration is bad. If I downshift to third gear, engine RPM goes up and problem stops. So I don't think it'sin the drive line.
None of this happens when engine is cold.
Done all the basics: plugs, wires, cap, rotor, air and fuel filter, PCV. I have methodically removed, inspected, cleaned and reinstalled one at a time: fast idle valve, starting valve, IAC valve, EGR valve.Ran heavy wire down throughEGR ports and vacuumed out debris(not very dirty). Cleaned insideplenum w/ throttlebody cleaner. Replaced a number of vacuum hoses (but not all).Nothing has made problem better.
Tried 93 octane but made no difference. Have always used 87. Several bottles of Chevron Techron fuel system cleaneroverseveral tankfullsdidn't help.
Never a check engine light nor are there any codes. Still getting 25-27 MPG on mixed driving loop.
I appreciate any help. Thank you for a great web site!

 

Your symptoms are classic for EGR ports partially blocked. The blockage of some ports forces too much EG into remaining open port/s resulting in overleaning and a stumble or miss. Clean EGR ports should fix your problem. See DIY for EGR Port cleaning.

good luck

 

TexasHonda.........THANK YOU! I almost fell over when I read the Honda Bulletin describing my problem. Won't be able to tackle this job for a few weeks, but I will let you know what happens. Thanks again!!!!!

 

A good way to verify the that's the problem is to disconnect the vacuum line to the egr valve and go for a drive. The hesitation should go away.

 

I am having same problem on my 97 SE. I cleaned the ports twice but did not help so I think there is something else bad. How you check EGR valve if it is bad. If I disconnect the vaccuum line from EGR valve should I have to block (close that port) the vaccuum at the valve or block the line which I disconnected. Thanks for any help.