Could use some help troubleshooting. Engine running rough.

[Loki]

I started running into this problem last Thursday after work. I started the car up and it immediately started sputtering. Also noticed a very low frequency vibration (<5 Hz) and drop in power. Symptoms persisted through the RPM range up to about 3500, which was the highest I revved to. Cut to the next day, the car runs fine. Then this morning the same things happened when I first started it and kept up until I got onto the highway past about 50 mph, at which point symptoms went away and there was a noticeable power gain. Didn't see anything obviously wrong with the engine and the exhaust smelled and looked normal while the engine was exhibiting this behavior.

Can anyone give me some tips on where to start troubleshooting? Thanks!

[Loki]

Did a compression test, cylinder one came back at about 50 psi, real low. Mechanic friend thinks it could be a bad valve, which means upwards of $1500 worth of work at a shop. I'm thinking maybe I could attempt the work myself after school starts in a couple weeks and I won't be driving the car as much. Anyone know how hard it would be the change out valves, or if it'd be easier to change pick up a used head and swap that?

[biggie]

I would try swaping valves. If getting a new head I would want to deck it, etc. Which would get into too much money.

[Loki]

I see a few rebuilt heads in the classifieds, I was thinking maybe I could find one that is good to go. In the end, I just want to do whatever saves me money.

[Loki]

Alright, I REALLY need NICO's help to try and isolate the problem. I don't really know where to begin troubleshooting this thing.

So, as it sits: the engine is sputtering and there is a big loss of power. Even at WOT in 4th I couldn't get above 50 mph going up a slight hill. The engine also shakes much more than normal. I took it to a Nissan mechanic I know for a bit, and when he tested compression it was 175 psi on cylinders 1-3, and 150 psi on cylinder 4. I took a short vid on youtube, maybe you can hear the problem a little:

[youtube]http://www.youtube.com/watch?v=kPm7NQNitpE[/youtube]

I need help pretty bad here. I'm going back to school this weekend and I need the car to be working.

EDIT: In case anyone ever reads this post and has a similar problem, turns out it was a bad fuel injector on the misfiring piston. Replaced cylinder 1 injector, runs fine.