Completely stock 1990 Civic Si. I have intermittent hesitation/stumbling/loss of power at low RPMs. It always starts easily. It never stalls. The check engine light is not on and there are no code blinking on the ECU. I started to follow the troubleshooting guide in the service manual. I am at the point where it says to substitute a known good distributor. Unfortunately I only have the one distributor. So I would like to make it "Known good" What goes bad? How do I test my distributor?

 

ignitor possibly failing or soon to fail.
I would try to replace the ignitor only, leave the dizzy just fix it up with new ignitor.

 

Even a cheap aftermarket ignitor is $50. Isn't there a way to test the existing one?

I found this when searching for the ignitor:

IGNITER UNIT
Check and service any Honda engine codes before proceeding.
Check the No. 32 50A fuse on 1985-91 models, or the No. 39 50A fuse on 1992-95 models in the dash fuse box before testing.
Remove the distributor cap, rotor and the leak cover.
Disconnect the wires from the igniter.
Turn the ignition switch ON.
Check for voltage between the BLK/YEL wire and ground. If there is no voltage check the BLK/YEL wire and ignition switch.
Check for voltage between the WHT/BLU wire and ground. If there is no voltage check the WHT/BLU wire and the ignition coil.
Check the continuity between the WHT wire and body ground. Service the wire or connectors as needed.
Check for continuity between the BLU wire and body ground. If no continuity check the wire and connectors between the igniter unit and the tachometer or the A/T control unit.
If any tests were not passed, replace the igniter unit.
Turn the ignition OFF.

 

and this..

IGNITION COIL

1990-91 Models
With ignition switch OFF, remove the distributor cap.
Remove the two screws to disconnect the BLK/YEL front terminal A and WHT/BLU from terminal B of the coil.
Using an ohmmeter, check resistance between terminals. Replace coil if resistance is not within specification.

Resistance will vary slightly with coil temperature. Specifications are at 70°F (21°C)
Check that the primary winding resistance between terminals A and B is 0.6-0.8 ohms.
Check that the secondary winding resistance between terminals A and the coil tower is 9760-14640 ohms.
If not within specifications, replace the coil.

 

Ignitor, my car did the exact same thing before. Replaced ignitor and doesn't bog or misfire in any rpm.

 

I have no continuity on the white or blue wire to ground. Its 34 degrees outside so my testing is in bursts of 30-45 minutes. Is there anything between the blue wire from the ignitor to the tachometer? I have gotten to the firewall and have continuity.

 

Have you looked at the MAP sensor? Make sure the vacuum line to it is good.