cylinder # 5 dead at idle

mechanic says i need to do leak down test to see if valves have carbon deposits on them , car only has 29000 miles on it & its a 1992, dirven by old lady >Can anyboby explain how to do leak down test, . if it is cARBON any way to get rid of carbon depoits without pulling head ? thanks fred

I'd look for a vacuum leak near that cylinder...

If the valve seating was bad enough to cause a dead miss, you'd see it on a regular compression test as a profound lack of pressure.

Could have a leaking upper-to-lower plenum gasket or something...try spraying around the manifold with some carb cleaner while it idles..if it sucks it into a leak, the idle will pick up momentarily...

you can measure the pressure in the cylinders when the engine cranks with the ignition wires unattached.
I'm not sure this device is available at regular autostores but it's very simple - a standard manometer gage that measures and "holds" maximal pressure equipped with rubberised end that fits the spark plug's seat.