When starting in morning, engine performs well. No problem accelerating to 70 mph and climbing steep hills. After long term high speed driving followed by stopping for 10 minutes, upon resuming trip there is 15 - 30 seconds of sputtering on the on-ramp (fells like fuel feed is discontinuous). Then engine lines out out and performs great and can climb 6% grade at 70 mph without any problem. Help!!!
When an engine is shutdown, the coolant stops circulating and carrying off heat from the engine block and other metal parts. The other things, like sensors, get hotter. The extra heat may lead the sensor to change, for the worse, until it cools again. The question is, “Which sensor?”. One way to find out would be to: run the engine until it reaches full temperature, heat select senors and actuators (like the Idle Air Control valve) with a hair dryer, or other heat source, and see if you can get the engine to stumble. When it does stumble (runs rough), you’ve found your culprit.