Low compression on one cylinder

2000 Grand Am, 3.4, 130km. Engine idles rough surging between 550-700 rpm. Picked up a code indicating misfire at cylinder no.2 , changed wiring around and sparkplug. Problem still exists, checked clyinder compression , down to only 85lbs. on cylinder no.2 , others are high. No coolant leaks showing exterior nor in the oil. Coolant level has not dropped at all. Applied air into the cylinder when piston was at T.D.C., could not hear air out of exhaust, slight air noise from air intake horn present. I tried spraying brake clean around intake gasket to see if there was a change in rpm, but it is difficult to get at the areas.Is the intake manifold gasket the cause or ?

Welcome to AF.

Sounds like a valve or your rings are bad, since the others are all high I would say its probly a valve.

Did you do the compression test dry or with a little oil ?
If you used oil did the compression raise ?