1998 Ford Ranger 4x4 4.0liter manual transmission 98000 miles, recently I noticed a hum, almost, coming from my engine I thought it was my air filter but after disconnecting the hose I discovered the noise was coming from either inside or behind the throttle body. It was really howling at me through the throttle body opening. When I engage first gear and put a load on the engine where the idle drops the noise goes away. Could it be a vibrating gasket or is it something more serious? I didn't think there were any moving or loose parts in the intake besides the throttle body. It is vibrating the whole air intake system, but get much less noticable if you move left or right from the center of air intake maniforld. I am not sure what could be causing this please help.
Well I just thought I would post the solution to my problem since no one else seems to know the answer and no one else seems to have had the problem maybe it will help someone down the road. The problem was my Idle Air Control Valve (IAC). When I touched it the vibration cut in half and when I unpluged it the noise stopped all together. I have been driving on the new one for a week now and have had no problems and My truck Idles way better. Before my idle rpms wouldn't drop below 1100 now they stay cool at 700 should save me some gas. Hope this helps somone down the road.