Hey Guys, I am not a mechanic and I just bought this 97 F150 5.4 V8. Had a couple questions earlier and everyone helped me out. When I have my truck at idle, approx 550 rpms I hear a slight rattle. Give it some gas and it goes away. Idle at stop light, rattle. I looked around and haven't noticed anything loose. Just had an alignment and brake job mechanic said everything was fine. It's just annoying...anything to worry about? Thanks for the help

 

im not quite sure what kind of rattle your getting but on my 4.2l it was the catalytic converter shaking a bit. I just used a metal strap to put a bit of pressure on it and it went away

 

if you rev it up when you're idling does it rattle when the engine is on it's way back down to idle? The inside of one of my catalytic converters was all busted apart and it rattled pretty noticeably at idle. I just cut it apart today and took it all out, truck runs a lot better now!

 

Might be your cats, could be the heat sheilds( made of thin metal) to protect your floor from heat from your cats. they are so thin they usually rust at the corners where they are rivited to the underside and rattle against the cats or exhaust pipes. If it is the heat sheild, use some short self tapping screws to put it back up. of course dont screw it through any wires!

Good Luck, Let us know.

 

wont that effect your emissions

 

Thanks ..It doesn't rattle until it the RPMs fall back down. Just had it inspected everything passed. Not very loud seems to be coming from the engine compartment, passenger side. I crawled under the truck and could barely hear it

 

It was a/c compressor changed it and everything quiet now