I have an 92 Integra (MT) with just over 200K miles. The last couple of weeks the engine has started to hesitate at roughly 2500 rpm and also 3500 rpm. It feels like the car wants to stall and then recovers. It will keep repeating this if I hold the engine at these speeds. I can even get the engine to do this if I rev the engine to this speed while stationary. All other engine speeds seem to be fine. It happens when the engine is warm or cold. No warning lights.
I have replaced the plugs, fuel filter and air filter.

Any ideas?