7 lb oil pressure (idle) on a 3.8 GM engine

My 3.8 (Grand Prix) yields 50 to 60 lbs of oil pressure on highway, which is ok.
The problem is: Every time I start the engine cold, the oil pressure
(measured with a mechanical gauge) is 7 lbs only. The sending unit as well as the oil pump itself have been replaced... without any improvement.
Anyone having a hint on what causes the problem?
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Clement,
There is no GM spec. for oil pressure at idle. The minimum psi for a a '98 G/P with 3800 engine is, (you didn't state your model year? This is for a '98. it should be close.), 60 psi at 1850 rpm, using 10w30 oil.
GMdude
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