1997 Plymouth Grand Voyager - Oil pressure warning light

I have a 1997 Plymouth Grand Voyager (140,000 miles) with an oil pressure warning system problem. When the van is idling or not being accelerated (going down a hill or slowing down for a stop), the low oil pressure warning light comes on and the warning alarm starts dinging. When I accelerate, the light goes off and the warning alarm stops. I just had a new transmission put in, and this was not happening before. The transmission shop could not find the solution. They checked the oil pressure and said it was fine. They replaced the oil pressure sensor and that didn't fix it. Another car forum suggested that it was the idle air control valve. I replaced that and it didn't fix it. I think there are some wires crossed somewhere. Sometimes when I unlock the door with the remote it turns on my windshield wipers for one cycle. I don't know if this is a separate problem or not. Any help would be appreciated. Thanks.