hard start

96 SL2. Thought I had all the bugs out but yesterday on 3 occasions with a warm engine the engine cranks fine but very hard to start. Looked at a TSB referring to this and it mentioned a string of DTC's. Well there are no DTC's and when it's cold it fires up perfectly. If you crank long enough when this occurs (10-15 seconds) it will fire up and than after a short time run well. Up to this point I have R&R'd the throttle body and cleaned. New NGK plugs (from the Saturn dealer) and new wires carefully routed and cleaned the corrosion off the coil towers. Ideas? Larry