1991 Accord running rough

1991 Accord w/160k miles, after engine reaches operating temperature, as I accelerate, the engine begins to run rough at precisely 1500rpm, then smooths out after passing 2000rpm. Any suggestions?

When were the spark plugs, air filter, and fuel filter last changed?

plugs and fuel filter about 30k miles ago, air filter about 6k miles ago

You are due for both spark plug replacement and fuel filter replacement.

For your sake, I hope that your fuel pump has not been damaged by trying to push gas through a partially clogged fuel filter.

I replaced fuel filter, spark plugs, distributor cap and rotor, adjusted timing. Made no difference, still has same symptoms.

Are you sure its pegged to an rpm range, or perhaps to a throttle position? These will, of course, often coincide, but try to sort that out. I don’t know if this thing will have a throttle position sensor or not, but you might check it if it does. You’ll need some specs for that and a volt/ohmmeter.

I’m absolutely positive it’s the rpm. In first gear (it’s an AutoTran) at 1500 rpm the throttle position is open much wider than when I’m in fourth gear at 1500 rpm traveling at say 40 mph.

I would move deeper into the ignition system - e.g. back toward the coil. A shop manual would be best for testing, but this will give you a start:

Add valve lash adjustment to your check list. I would do it every 30k miles on this engine.