"Vibrating" idle problem finally solved! It was the muffler resonating.

[mikepier]

I have been troubleshooting a "vibrating" idle on my 99 SOHC for the longest time. To recap, my truck starts and runs great. Idles fine when cold, but once it warmed up and if I was stopped at a light, I would get this "cyclic" resonating vibration in the truck. I ruled out the IAC,MAF,plugs,wires and coil. So today I decided to go under the truck while it was in gear, had put on e-brakes and blocked wheels. What I found was the drivers side catalytic converter vibrating. So I used my floor jack with a piece of wood and put it directly under the cat, and raised up the jack enough to put pressure on the cat and cause it to stop vibrating. Guess what, the vibration was gone! I sat in my truck and could not believe it. All this time I thought it was engine related. So now I have to rig up some kind of clamp to brace the cat a little, or perhaps maybe just remove the heat shield altogether, as I believe that's the root of the problem.
So for those of you who have the same problem, try using a floor jack and see if the vibration stops,

 

[BrooklynBay]

You could replace the exhaust hangers.

 

[mikepier]

You could replace the exhaust hangers.

The exhaust hangars by the mufflers are still good from what I can see. I don't see any hangars by the cats, unless I missed something, or maybe they broke off and I did not know. I'll check again tomorrow.

 

[mikepier]

Not fixed!

The exhaust hangars by the mufflers are still good from what I can see. I don't see any hangars by the cats, unless I missed something, or maybe they broke off and I did not know. I'll check again tomorrow.

I did not see any hangers on the cats. There is one hanger after the cats on the double pipe before it goes into the muffler. I tried bracing the cat to the frame, but that made the vibration worse( probably because now the vibration was being transmitted to the frame).
It appears that the cat itself is not the cause of vibration. Something in the engine is causing the cat to resonate, so its back to square one now.
The existing hangers on the muffler and resonator look good. I don't know if those rubber insulators go bad after time.

 

[96eb96]

I did not see any hangers on the cats. There is one hanger after the cats on the double pipe before it goes into the muffler. I tried bracing the cat to the frame, but that made the vibration worse( probably because now the vibration was being transmitted to the frame).
It appears that the cat itself is not the cause of vibration. Something in the engine is causing the cat to resonate, so its back to square one now.
The existing hangers on the muffler and resonator look good. I don't know if those rubber insulators go bad after time.

heat shields? All my fords have metal worm clamps on the exhaust or cats to stop noise.

 

[239]

I know this is an old post but did you ever figure this out? My explorer's going through the same problem. My local shop said the exhaust wasn't on the hanger. They put it back on and it stopped but now it's back again.