Get the vehicle to an intelligent mechanic. The on-board diagonistics are sophisticated and should be able to tell an intelligent mechanic where the problem is.

A compression check should be done to rule out a piston/valve problem (most compression problems occur gradually, not suddenly as in your case); absent a compression problem any fix should be non-major.

If you've had no serious mechanical problems to this point you've got a mechanically good engine and the dealer would just LOVE to talk/scare you into trading it in; don't do it; it's fix-able.

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A good pessimist is never dissapointed!