Hi. I bought my 2nd Saab a few weeks ago (2003 9-3 aero with 78K miles) for what I thought was a good deal bc of the leak on the heater bypass valve. When driving the car home it got a little hot, added more water and it run fine. After replacing the valve notice high pressure on the reservoir. Bad head gasket! Run some blue devil gasket sealer through it and fix the problem but I noticed irregular idle. The check engine light came on with the codes p1549 (charge air malfunction) and p1303 (missfire on cylinder 3) and drove it for about 100 miles until I found the broken vacuum hose to the turbo. After fixing it little or nothing changed and still idling rough (not too bad, like a Subaru or boxer engine). Performed a compression test and got about 150 psi (conpression tester is missing the check valve so it doesn't save the pressure) on cylinders 1, 2, *and 4 and 30 psi on cylinder 3. Tried again with some oil and the compression did not changed. Now my question is : does this sounds more like a valve problem or a cracked piston? And how can I check it?