I have a 95 f-350 with the 5.8. lately I've been getting a loud roar from the throttle body. It started happening at idle and usually after engine is up to temperature. Now it is doing it more at different speeds. the air temperature has gotten hotter to, not sure if this has anything to do with it. If I disconnect the IAC the noise stops. put it back on and it starts again. Want to see if anybody else has had this problem or any idea why its happening.

 

When you disconnect the IAC the idle RPM should drop to the 400-500 range or stall. If the RPM stays the same or does not come close to the above you have a vacuum leak.

 

When I don't have this noise happening the truck runs excellent with no signs of a vacuum leak and this still doesn't explain the loud noise which is hard to describe. A loud vibrating hum is maybe a better description. The truck had a cold air intake on when I bought it witch does cause some noise. Now magnify that a lot louder and that's what it sounds like