The oil light comes on when the van is in idle, but not all the time mostly after driving awhile. All the fluid levels are ok. The oil & filter was just changed a couple months ago.

I think this is the oil pressure light not the low oil level light, so have the oil pressure tested by a shop and make sure it is within specifications or serious damage to the engine will result. If the pressure is ok then replace the oil pressure sending unit it is faulty.

It may be your oil pressure transmitter switch at fault. There's many different oil pressure transmitter switches. Here are some generic images:
oil pressure transmitter switch Google Search
It could also be that your vehicle is due an oil/filter change.
Is your oil level ok?

It's unlikely to be your oil pump at fault.

1. Check your oil level
2. Is the vehicle due an oil/filter change?

The oil pressure transmitter switch simply tells the engine 'low oil pressure'. This usually happens at idling speed due to a faulty transmitter switch, low oil level or there's a need for an oil change as the old oil is no longer up to the job. Oil pressure switches are easily changed.

The important thing is that you aren't getting a warning light when driving at speed. If your oil level is okay and it isn't due an oil/filter change - it probably is the oil pressure switch at fault.

For your own peace of mind try adding an oil additive.

First check the oil level. pull out dipstick with engine off, wipe, and re-"dip" it to see . If the level is O.K., it may be serious . See a mechanic.

Action: Description

Inspect Cooling system hoses
Torque Body Fasteners
Inspect Idle speed
Inspect Exhaust system heat shields
Inspect Fuel lines
Inspect Emission System
Torque Frame Fasteners
Replace Air filter element
Inspect Drive Belt(s)
Change fluid Automatic transmission/transaxle
Inspect Parking brake
Inspect Ball joints
Drain, flush & refill Cooling system
Inspect Steering system
Inspect Brake system
Inspect Brake lines & hoses
Inspect Axle Shaft Oil Seal
Change fluid Rear differential
Inspect Driveshaft Universal Joint(s)
Inspect Constant Velocity Joint Boots
Change fluid Brake system
Replace Crankcase Oil Filter
Lubricate Door checks
Inspect fluid level Manual transmission/transaxle
Inspect fluid level Front differential
Inspect fluid level Transfer case
Inspect fluid level Rear differential
Change fluid Crankcase

Try removing the idle speed motor on side of throttle body, and spray it clean, as well as the port it came out of, with throttle body spray cleaner. Don't pull and extend shaft of idle motor, just leave it in position it's in, and make sure you don't lose small "O" ring on idle motor. Re-install and try it. If it cures it for a while, then starts to do it again, replace the idle speed motor.

some cars with oil level warning light on, it doesn't mean that its only reading the engine oil level is low, sometime the transmission fuid too. Did you check your transmission fluid if it is ok or not? try to check and let us know, ok.

change oil pressure switch it' should be near the oil filter

You need to, at the minimum, change the fluid & trans filter. Easy proceedure. With van jacked up & blocked so it won't fall, use a large collection tray under trans pan & remove pan bolts. let oil drain into tray. use screwdriver to pry pan off. clean pan thoroughly & trans matting surface. Remove filter. You may need to adjust low rev band. Check with dealer or parts store for proper clearances. Put new filter on & tighten bolt[s]. Use new gasket & rebolt pan. Use gasket sealer on pan side only. You'll need 4-8 qts. of the proper tranny oil. Fill through trans. filler hole. Start engine & let warm up, check level & don't overfill or you'll have to suction out until level.

When was the last time you had transmission oil changed and the tranny pan removed and the tranny filter changed? If never, this is your starting point.

The problem with these vans is that the tranny pan is at about a 20 degree angle under the transmission near the driver front tire. The problem with this design is that these pans eventually begin to leak at the lowest point of the pan, and over time you will not notice the ATF loss. Most likely your ATF level or cleanliness/viscosity may be bad.
Don't cry 'TRANSMISSION' until you get your tranny serviced (ATf oilc change, new tranny filter, clean magnets, clean pan, clean tranny).

You do not say if the oil level is ok, or if there are any related problems. Assuming the oil level is OK, it is a very simple system, There is a pressure switch near the oil filter, check the wire from this is not chafing/rubbing on the engine anywhere. If it appears OK, wait until the light is on, take off the connector carefully and check the light has gone off. If the light goes off the pressure switch is faulty. If it stays on you have a short circuit somewhere between the switch and the warning light.