RESOLVED: Vibration problems after valve cover gasket replacement

[X53Jay4.8is]

Originally Posted by fishhouse4

Long story...have had my 06 4.8is for a few months. Had an oil leak at timing case cover and valve gasket so took the plunge last weekend to replace both valve cover gaskets, both timing cover gaskets and all seals/o-rings encountered along the way. Also replaced spark plugs, drive belt and leaking coolant expansion tank.

Job was a total PITA - first took 2 full days. Once we started it back up, I had a VERY bad vibration at idle, white smoke out drivers side exhaust after idle for a few minutes, much louder engine/exhaust growl and delayed throttle response on the low end. Like rattling your teeth out bad...sounded like every piece of plastic in the dash as going to shatter apart. Calmed down when you gave it gas and better at highway speeds. No codes or SES.

Figured I had a vacuum leak on the drivers side valve cover (was some oil on the back side again). So I pulled VC back off Monday to re-seat. Resulted in vibration at idle much better but still ALOT worse then before any work. Throttle was maybe better then prior to any work. Still louder at WOT then originally - but in a good way (wouldn't need that X-pipe I had previously wanted to get just a little more growl).

Unwilling to accept defeat, I pulled the drivers VC back off a THIRD f'in time today to re-seat. Results about the same = much more felt vibration at idle and low gears and louder then before I did any work. Seems fine at highway speeds. Noticed vibration is worse when I turn on the AC at idle.

99% sure I got the VC nice and tight this time (will test of oil leak once it cools down later today). Just not sure if the problem is from a vacuum leak (and where?!), plugs, drive belt, etc. I have quadruple checked all wiring/plugs and hoses.

It idled like a normal car before. I just don't know if this is normal or not. With new plugs, clean VANOS (that were crazy dirty), new belt...maybe this is the way it's supposed to feel? What/how do your 4.8/4.6is's feel and sound at idle?

I'm out of ideas and incredibly frustrated at this point having spent probably 30-40 hours dealing with it. Anyone have ideas or experienced something like?

Here's a video from interior (hard to hear the vibration from video...but you can tell it more when I turn on AC).

Here's a video from engine bay.

Okay hate to say this but if the vehicle was running smoother before you did all this work then there is something wrong if the idle is worse and vibrations are present after doing all the work. Check to make sure no ground wires are off, coil packs seated correctly. After all that has been checked you might need to get the engined smoked to see if there are any gaskets leaking causing a small leak.