2.7L engine. After driving for about 10 minutes, why does it stop, rpm drop below 500 for about 5 sec. and oil light flickers, then returns to normal idle?

You need to find out why you have low oil pressure. It is normal that as engine rpm's increase, the oil pressure will rise- the oil pump is moving oil faster. Even though your light goes out, you could still have critically low oil pressure. There should be sufficient pressure at idle to keep the light off. The light will come on when your oil pressure is almost nil- I believe for some it's as low as 8 psi. Normally, oil pressure at idle is specified anywhere from 15 to 40 psi. You would have to check specifications for your Expedition. To verify oil pressure, hook up a mechanical gauge at the oil pressure sending unit on the engine block. Check with a local shop.

The causes run from easy, simple to budget busting ruin. Low oil level, wrong grade oil, real old oil, oil leaks, internal oil leaks, worn oil pump, worn crankshaft bearings. It was pretty common on older very high mileage cars to have a fluttering oil light at stops and idle. It was time for a rebuild, or time to look for another car.

get an engine flush run the engine to hot ,then drain the oil .do oil and filter change.

check oil pressure switch located on side of engine block. not sure what side on a neon.

Test the oil pressure, if too low, repair the engine, if normal replace the pressure sending unit .

could be numerous reasons. this is your best bet take it in to a mechanic and have your engine codes scanned. it is a minimal charge, some even do it for nothing it only takes 10 minutes.this will point you in the right direction.

Increase the viscocity of your oil. If you're using 10W30, go to 10W40. If you're using 10W40 switch to 20W50. Don't use single weight oil.

with a 2002 Concord 3.5 V-6, what should the rpm be at 60mph? 70 mph?

I'm not sure if the overdrive gear is lost in the tranny, but the transmission light is on.

Thanks

have the engine wire harness checked maybe a communication problem between modules.

Sounds more like the Throttle Position Sensor or another sensor is letting the engine RPM's drop too low. When the RPM's are too low, the oil pump is not pumping enough oil.

you might try and change the pcv valve, my car hand a similar problem in the summer and i never changed it. the pressure blew my cam seal and i was leaking oil like crazy. i dont know if it will fix it but they are cheap. i would give it a try.