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Q: Is it the oil pump? on 1994 Chevrolet Cavalier

When my cars engine warms up the oil light comes on when i pull it out of gear or when i am up shifting through the gears it comes on breifly but goes out when the engine idles higher. i think it might be a low idle but others tell me it might be the oil pump going out. There is a steady knocking noise after it has been running for 30 min. at low idle. Like at a stop sign. And get this, it even runns smooth. So any ideas of what it could be?
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I was going to suggest testing the oil pressure with a test gauge until I read about the knock noise. If it's low pitch and coming from the lower end of the engine, I think you have worn out crankshaft bearings, whether all or just one, whether connecting rod or crank main bearings, I'd have to hear for myself (mains are more of a clunk sound, rods more high pitch rap).
You could pull off the oil pan and examine the bearings and crank. If the bearings are worn to the base metal, they're shot and if the crank is still smooth, you could try replacing all the crankshaft bearings, rods and mains. This is a cam--in-block engine design and the cam bearings probably are worn too. You can lose a lot of oil pressure from worn cam bearings which would require a major engine teardown to repair and wouldn't be worth it.
The knocking noise at low idle sounds like crankshaft main bearings to me, A loud and scary rapping noise on acceleration would be rod bearings.
Either way, I'm leaning toward finding a guaranteed used engine at the auto parts recycler (junkyard).
It's the knock that causes me to swing that way, using a replacement engine. Even in a fairly bad case of knock, it's sometimes possible to save an engine for a while with new bearings and oil pump but it's your call depending on how you feel about how you ant to spend your money. The engine isn't worth rebuilding, if you like the car well enough, a guaranteed used motor is a good way to go, if you're broke like I've been too many times, desperate measures like replacing the bearings and pump are a choice but it you couldn't depend on it unless the crank was in good shape, but that's not likely if it's been knocking.
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