I have a 2000 F150, std cab, 4 speed manual, 4.2 V6 that exhibits a shudder at idle (slightly worse with the the AC on) and a rattle from under the vehicle. I was told the rattle may be from a loose heat shield, but I inspected this and can find no problems - all is tight and there appears to be plently of clearance. Otherwise it runs great and I am getting 19 MPG. The check engine light is not illuminated and I have changed the PCV valve. I have heard the rattle on another F150 and suspect this may be a common problem.

Any help would be appreciated.

 

OMG, someone else with the same problem!!! yay!!! Well, wait, it's a problem, why am I celebrating?

Anyway, ya, same noise and vibration. Only happens at really low rpm, like 550-600. The only time I see that low is in drive at a stop, after it's all warmed up. It just got worse too, so I'm dyin to figure out what it is. I crawled all under there and started pulling and pusking on plates etc, and everything seemed gtg. I even sprayed the entire underbody with a coating bout a year ago, that should help!

If anyone has any tips, we'd both appreciate it!

 

ok, thought I was crazy and the only one with the problem, but with justification, I went to the blue oval boys today. Didn't leave my baby there, I've learned that lesson, but I just went in to ask a few questions.

As for the rattle, if all else under the body is good, he said it could be the catalytic converters. Uh, oh, now were talking a few hundred bucks here... Anyway, he said to take a rubber mallet to them and see if they make the same noise when you give em a good tap. Da man said that the platnium (sp?) elements could have broken loose, so time to replace them. He actually said not to have ford do it, way too much $$, I'd guess like over a grand. I know K&N makes em, along with many other companies I'm sure. looks like I might go that route and take them to the local exhaust shop to have em swapped out. Crap, if they're direct replacement, even I could do that!

 

did you guys check under the converter heat sheild? there is a silly tag on the converters tack welded in one spot and then they wrap the heat sheild around them. i've had these tags break free and cause a noise similure to the one you are talking about i think. i had to pry the vents on the sheild and use a thin needle nose to get those tags out and i also wrapped a hose clamp around each converter just so i knew the heat sheild wouldnt start rattling. and then all was good.