I'm trying to figure out if a slight roughness in my 2.1 is normal and, if
not, what might be causing it. This is a recent rebuild with many parts
replaced, and my mechanic says he thinks it is running normally. I'm not
sure. Here's what I observe:

- while driving, as the revs rise to about 2200 there is a slight roughness
to the engine that seems to get less as the revs go up to about 3000 and it
seems smooth above that

- with the car stationary, I rev the engine slowly and as it reaches 2200 a
distinct roughness sets in and simultaneously the revs rise to 2600 without
any further movement of the throttle, then opening the throttle more the
roughness gets less towards 3000 rpm.

- with the oxygen sensor disconnected (and in the minute or two before the
ECU reacts to that) it does the same thing but a little less rough, which is
interesting because it shows the behavior is there with the ECU in open-loop
mode (if I am understanding/describing it right).

- all the above is with the engine warm; when cold it does not exhibit these
symptoms.

- idle is normal, steady at about 900 rpm

Is this vibration between 2200 and 3000 rpm normal for a 2.1L (1990 Westy)?
If not, what might be causing it? I did not notice this behavior before the
rebuild, but the engine had lower compression then and possibly it may have
been present but at lower intensity and I didn't notice it.

Things that were replaced during the rebuild (and therefore they are
suspect, right?): distributor/cap/leads, plugs, O2 sensor, injector seals.

Things that were not replaced (and therefore might be assumed to be OK):
coil, ECU, injectors, air meter, idle controller/valve, voltage regulator,
throttle, fuel pump, fuel distributor tubes, injector control relays.