I bought a ranger with a etec 225. It's an 06, every now and then when I unload it off the trailer I start it up, back it off with out touching the throttle, idle to the dock or what ever. Now when I get back from parking the truck. I idle out to take off and when I hit the gas it has a deep tone but no power. No higher on rpms or anything, kill the motor start it again and I hit the hot foot and all the power is there. After I do that I'm fine for the day. Any ideas on what could be causing this?