Rough idle on an otherwise smooth EJ22 w/ 234k miles.....

[silence2-38554]

Hey all, trying to troubleshoot the motor in a high-mile Legacy I recently picked up. The engine seems to be very happy anywhere above 700 RPM. Once it tries to idle any lower, like around 500, it gets really rough. You can even start to hear something bad going on inside, like a quiet knock. When I say rough, I mean it's hard to talk while sitting in the car without your voice jumping. ROUGH. I've run seafoam through the PCV, replaced the PCV & plugs w/ stock spec NGK's & replaced the fuel filter. Anyone have any ideas as to why just the idle would be this rough but then at all other RPM feel totally fine up to redline?

[Legacy777]

What year Legacy? Is it AT or MT?

[silence2-38554]

1990 Legacy, AT

[Legacy777]

Are there any codes stored in the ECU?

Have you done a vacuum check at idle? There may be a vacuum leak somewhere that is causing the problems.

You can try spraying starter fluid around areas where gaskets are and see if the engine revs up.

[silence2-38554]

Good call on the potential vacuum leak, will check that out tomorrow.