I have a 1990 Legacy wagon, 120,000 miles ran like a champ until about a year ago. I took it to a machanic and he replace the Ignition relay and it ran for a year and it stopped running again. I replace the ignition relay and it ran for a couple hours now it runs for a few minutes and while its running the tach bounces like a tennis ball. I am guessing that it is the ECM but I am hoping that there might be something else to try.

Is the check engine light on? You might want to see if there's any codes stored in the ECU. Instructions are on my site under the notes & tips, engine related section.

Thanks, I will give it a try, now I know what the odd plugs under the dash are for.