1996 Mazda Truck Idle problem

I have a 1996 Mazda b2300 2.3 manual trans. 153,000miles Truck runs pretty good with the exception of the following problem. After going down the freeway or just driving to the local store, when coming to a stop and or just coasting in neutral the engine idle goes to about 1500 rpm for about 10 to 15 seconds and them goes to about 1000 rpm and goes gradually to about 800 rpm. Recently replaced the EGR valve, solinoid, and pressure sensor. Althought the parts house gave me the wrong egr valve at the beginning. The service engine light is not on now that the egr system has been replaced. Need some direction on where to start.