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I’ve got a 2.5l Subaru that is very shaky at idle. Did a vacuum test and the gauge needle shook rapidly between 10-14 inhg when idling. Just replaced all 16 valves and head gaskets and adjusted the valve gap so I don’t think those are the problems. What are your ideas?

2002 Outback 146k miles automatic.

All valve springs were replaced as well. It does throw p0302 and p0304 intermittently

2 Answers

Have you checked compression?

Just had a compression test done. cylinders 2 and 4 are giving about 110psi and 1 and 3 are at 175

Yea I think they are suppose to be within 10 percent of each other and I dont think that is 10 percent. Did you do it yourself or take it to someone?  Sorry if I am incorrect I know on a boat motor its 10 percent.

General rule of thumb is cylinders should be within 10 percent. This is not even close. I can see where that large difference in compression would make for a shaky idle.


Did you replace the springs?


shaking would indicate misfiring. See our FAQ for more information on that.

Yes I had all the springs replaced