Thank you for your help in the past....I now have another problem.

I have a 99 4.6 with 205,000 miles (rebuilt a year ago). About a week ago I started noticing what seams like valve clattering. It only occurs when the truck is at operating tempreture (It's fine when it's cold). It also only occurs between letting off the accelorator, and giving it gas. right in the middle range.

If I am sitting still at Idle, it occurs when I turn the steering wheel side to side. It doesn't sound very good at all. When I pull up in the parking lot...my friends ask if my truck is a diesel?

Please help!

 

check and make sure your oil level is good

 

The oil level is good. I changed the oil from 10W-30 to 10W40 thinking the oil was too thin for the 100+ degrees here in Tucson.

A few hours ago, I filled up with premium (91 octane). It seemed to help alot, but I can still hear it a little.