Low compression prblem

Alright I have a 1992 Lumina Z34 thats been running rough for a little while, me and my dad replaced the motor about 8 months ago. It was running fine for a little while then started running rough. When the car is cold, I have to feather the gas to keep it from dieing. Also when it is cold when I try to accelerate is lags real bad, then all of a sudden just takes off. I got new plugs and wires on the car and when I did a compression check all of them came up 160 except for the #5 cylinder which bounced around. I tested the #5 a bunch of times and got a range from 15 - 90 and I got 180 on it 1 time. 60 was the average. Does anyone know what would make the compression jump around like that for that cyclinder? Also when I rev in park I cant get past 3300 RPMs just bounced off. Any information would be greatly appreciated. Thanks

As far as the compression issue, I'd run a leak down test. I'd suspect something in the head/valves. Maybe a bent valve???

it could have a rev limiter while in park. My 2001 lumina has one at about 4000rpm's. I also suspect a valve isnt seating correctly, or is bent. Did you check the timing lately? Could the timing have retarded. I hear that if a belt retards by one cog, that the motor will run, but will run very very bad. But I suspect that the valve isnt seating correctly. Change your oil.

Thanks guys, changed my oil a few days ago didnt notice a change in how it was running. How do you perform a leak down test? Thanks again guys :)

hope it all works out for ya