My 2005 Subaru Outback shakes, rattles, rumbles and vibrates on the freeway - ONLY after it’s warm, after about 40 miles, and only when I step on the gas. As soon as I release the gas pedal it’s back to smooth sailing. As soon as I engage the accellerator the entire front end shakes and feels like the wheels are about to fall off. It’s much more noticeable when going uphill-
I have 150k miles on it,and the guy I bought it from put in a used motor @ 127k. The motor mounts were recently replaced as well as the timing belt change.
There’s not enough info known (CEL on, any codes present, etc) to make much of a guess.
A used engine is always suspect unless someone has run a compression test on it. Point being that if this is an engine performance problem it could be due to any number of things.
Hopefully it’s not due to the valve lash tightening up on an exhaust valve due to engine heat and creating an engine miss.
IF (key word) the problem is related to the loss of valve lash due to thermal expansion of the metal in the engine this can create an engine miss and possible engine damage, all depending on which valve (or valves) is tight, how long it’s been going on, etc.
IF (again) there are no engine codes present and the fuel pressure is fine then I would run a compression test on a warm engine. If there’s an abnormality on a cylinder then that cylinder should be retested with the wet method; meaning a small shot of engine oil is added to the cylinder and the compression is retested.
If the compression does not rise much that can point to a cylinder head valve seating problem, which means a lash and/or valve burning issue.
Sorry I can’t be more precise but there’s a lot of blanks as far as the info goes.
I’m having a very hard time seeing this being a mount problem because if that were the case it should not be temperature or time dependent.
One thing that is quick and easy to do before running a compression test could be to connect a vacuum gauge to the intake manifold. A vacuum gauge will reveal in seconds if there’s a tight lash issue, timing belt off a tooth or two, clogged catalytic converter, etc.
Hope some of that helps anyway.