1999 explorer 4.0 cold rough idle

Clean or replace the IAC valve.

Hi, I'm french and I don't know what is IAC;wich total words please ? because it seems the same problem as mine (1998) Claude

Idle Air Control valve. It sits on top of the intake manifold.

i changed my iacv. no change any other possibilities?

Replace all plugs and wires with brand new ones before troubleshooting. When the engine is cold and running disconnect the IAC valve - does this change the idle or cause the truck to stall? If yes the IAC is working. If No, you could have a bad PCM output or wire harness short/open (you already changed valve). Also check that the bypass to the IAC is not plugged. On the Explorers with the EEC-V computer aprox. 97 and up, the computer had to be reset when changing the IAC valve. Disconnect the battery for 15 minutes then reconnect, the computer will retrain it's settings after 15 minutes worth of idling. Also check for any trouble codes, the EGR valve needs to be functioning properly before attempting to fix any idle problems. Another possibility is an air leak on a vacuum hose, so check for leaks, cracks or loose fittings. Good luck.

If you have the sohc engine its probably the intake gaskets. They expand when engine gets warmer and seal better

Spray some t-body cleaner around your intake gaskets and see if that make it run better