weird idle

So yesterday I got a few things done on the van. Changed the waterpump, thermostat, spark plugs, wires, PCV valve, distributor cap, rotor, coolant sensors, oil pressure sensor and got a crack in the radiator welded. So now the temp gauge works and the oil pressure gauge isn't going crazy anymore. I thought all was well until last night when driving home, I noticed it was idling funny. It kinda stumbles and I notice the oil gauge appears to go down when it does stumble. I got home and parked. This morning I started it up and it was fine, Idling smooth. I drove it to see what would happen and after a few miles plus stop at store, it started again. It doesn't seem to affect driving performance but when I stop at a light, I feel it. Any ideas where to look?

So yesterday I got a few things done on the van. Changed the waterpump, thermostat, spark plugs, wires, PCV valve, distributor cap, rotor, coolant sensors, oil pressure sensor and got a crack in the radiator welded. So now the temp gauge works and the oil pressure gauge isn't going crazy anymore. I thought all was well until last night when driving home, I noticed it was idling funny. It kinda stumbles and I notice the oil gauge appears to go down when it does stumble. I got home and parked. This morning I started it up and it was fine, Idling smooth. I drove it to see what would happen and after a few miles plus stop at store, it started again. It doesn't seem to affect driving performance but when I stop at a light, I feel it. Any ideas where to look?

Check for engine cylinder miss.
Crossed plug wire?
Any check engine lights?
Any vacume lines bad?