1999 Oldsmobile Aurora Hard to start when warm

My 1999 Olds Aurora with Northstar V8 (138000 miles) starts hard when the engine is warm and has been sitting for more than 5 minutes. When the engine is cold it starts right up. When the engine is warm and I start it immediately after turning it off, it starts right up. When the engine is warm and I let 5 or more minutes go by, it will not start unless I give it a little gas while cranking. It takes atleast 5 seconds of cranking to get it to start and the exhaust smells like it is very rich.

I replaced the spark plugs and wires with no improvement. The check engine light has not come on.