My Haynes manual says that 170psi is standard, and 128psi is the minimum. Here's some more information from Haynes:
"A low compression reading on the first stroke, which doesn't build up during successive strokes, indicates leaking valves or a blown head gasket (a cracked head could also be the cause). Deposits on the undersides of the valve heads can also cause low compression."
"If the compression increases significantly after the oil is added, the piston rings are definitely worn. If the compression doesn't increase significantly, the leakage is occurring at the valves or head gasket."
"If one cylinder is about 20% lower than the others, and the engine has a slightly rough idle, a worn exhaust lobe on the camshaft could be the cause."
Hope this helps.
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