97 GC AWD: starts, won't idle
 

I have checked spark plugs & wires. Then did a compression test that seems to show no compression in center back cylinder. So now I want to pull the intake and valve covers to maybe see why. First step: drain coolant. I turned the valve at the left bottom of the rad - nothing comes out. Rad is full. Tried air back into valve but it acts blocked. Ideas?

does it miss when you rev it up? If you have no compression you should have a dead hole and a misfire but it should still idle. As for the radiator, did you turn it far enough? The drain plug kind of unscrews from the radiator.