Need help!

[Messerschmittbf109]

I put Mobil 1 fully synthetic oil into my impreza for the first time( I used conventional oil before). Anyway, I took it for a test drive and the engine has no power what so ever. Everytime I go into the higher gear the engine sufficates and runs very loud. I did not do anything else besides changing the oil filter and oil; it was running perfect before the oil change, now I am affraid to drive it so I do not damage the engine. Has anyone had something similar happen to him? Any suggestions what might be the cause of this wierd behavior? Thanks

[freakray]

Did you overfill or underfill the engine with oil?

[Messerschmittbf109]

According to the Subaru owners manual the capacity is 4.2 qt. First I put 4 qt. started the engine until it reached normal temp. then I turned off the engine checked the oil level and added about 1/2 pint. After I did this I checked the oil level and it was within range. I though that putting to much oil could potentially cause my engine to run so rough. So, today in the morning I drained the oil and refilled it again with only 3.75 qt since I did not change the oil filter I figured probably there is around 0.25 qt in it. I guess I should check the spark plugs to see if I have any oil on them which would mean I have blown a gasket; however, I see no leaks anywhere. Now that I think of it I also changed the air filter. Maybe the air filter is causing all this mess, but if it is this would be the first time I had something like this happen due to the air filter. I also thought maybe I should flush the engine and try again, I may do that. although Mobil said no flushing is required. I don't know.