Mitsubishi Repair: Oil pressure light flickering 98 galant, weight oil, car idles

Question
I just checked the receipt and indeed 10/30 oil was added. We check online and found there are many similar cases with Oil pressure warning in low speed and idle status. One thing we don't understand is that if the oil pump caused this warning in low speed, why it didn't cause similar warning in idle status in our car.  Thanks.

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-----Question-----
the oil pressure light turns on when our 98 Galant is driving at the low speed. However, it goes off when the car idles or runs at normal speed.the oil level at dipstick is ok, and we just had the oil changed a month ago.
Is there anything else we should check?
thanks
-----Answer-----
Lucy: What kind of oil was put into your car? A lot of shops are useing a light weight oil. And most of these older cars don't care for that. So did they put in 5/30 weight? When you should have got 10/30. I know my older car likes the heavy oil and if I get lazy so let someone else change my oil; they will put in 5/30 then my oil light will come on lightly. So see if that might be your problem. Other wise your oil pump could be fixing to go out. But I am hoping it is the oil being to light. When you have car's oil changed always ask for 10/30 weight oil to be put in. And don't let them tell you that the 5/30 is better for your car. Because it isn't and it is just a way for them to save a bit of money. Hope this helps and good luck!

Answer
Lucy: When the car is just idling it is not causing the oil pump to work all that hard. The car is just sitting there running, but not pulling a load. But then you put it into gear and take off, then the oil pump has to work harder and so then is when it will show it's weakness. Hope this helps and good luck!