I have a 1999 Explorer sport 4.0 SOHC. When it is cold outside (below
50 degrees)and the car sat overnight or sat for several hours it wouldn't idle worth a darn, would rev up real high then sputter then idle high again, and it would die . It would do this for about 3 or 4 minutes then would idle great. The check engine light was on codes said bank 1 bank 2 fuel too lean. We changed the following IAC, O2 sensors, egr valve, air filter, spark plugs,mass air sensor,fuel filter. We changed the o-rings(gasket) on the intake and it FIXED the problem. The o-rings are rubber(like a thick rubberband) and when the motor is cold the the rings were hard and it caused a vaccuum leak, and when the motor warmed up they loosed back up. You can purchase these o-rings from the dealer you will need both top and bottom gaskets bottom rings run about $11 or $12, and the top gasket is $7 or $8.