Engine surges then dies

I have a 1994 Isuzu Rodeo which has recently had a tune up a amp sensor replacement and an O2 sensor replaced vehicle seemed to be Idling erractic 1500 RPM after startup which by the may come after one turn or several long turns to crank, I can recreate a condition over and over where the vehicle can be rolling in a parking lot then I can shift it into nuetral as the idling is erractic and the engine dies problem is it dies during normal operation also under same condition. it seems to happen in the lower range when the engine is ilded down due to a down shift in the transmission as when you're slowing down to stop only it continues to drop the rpm s all the way to zero, any ideas?