Is the vibration coming from the engine or the seat of your pants? If its from the engine the grommet may have bent a valve or smashed close the spark plug on one cyl. If the vibration is from the seat of your pants its likely a u-joint or a rear wheel bearing.

 

It is a seat of the pants, almost like a shimmy, but only under acceleration. IN neutral I can hold the RPMs' at the same as when I get the vibration while driving and there is no vibration at all. There is no unusual play in the rear wheels or the u-joints. I'm pulling the valve covers off tomorrow to see if I can see anything. I have pulled the spark plugs, they are all ok. The thing that is really screwy is the overhead MPG indicator went from @16.5 to around 12...

 

Good man, fix that and then start hunting for any other problems.

 

Im also going to get a leakdown test kit. that will find a bent valve. still hard to believe the motor is not experiencing other symptoms that would accompany a bent valve (missing, running lean/rich, etc)

 

well if its very slightly bent you may not notice it missing. but it will only get worse...
the thing that realy makes me think its your engine is your mpg drop. you sure your not running rich

 

I agree Sean, the description and symptoms point towards a warped valve. I certainly hope not. If he runs the bore scope and get the grommet out and there is no loss of compression he might get lucky. I certainly hope so.

 

should throw a code if the air/fuel ratio is that screwed up, right? and that little piece of grommet should be long gone by now. even if it hung around in the cylinder, it would burn up quickly....are there any external marks to line up so I know I'm at TDC for each cylinder when i do a leakdown test?

 

I've read on other forms they should burn up, I remember such a thread in DT a while back. I know of a Tacoma owner who sucked his TB gasket into the engine and got caught in the heads. Everyone was telling him it would burn up. He pulled the head and removed one severly deformed tb gasket. Could and should don't always happen man.

For the leak down test.
http://www.max-boost.co.uk/max-boost...own_tester.htm

 

when yopu put the compression tester line in put your thumb over the end and turn the engine over right when it stops pusshin air out yoiur at TDC if it starts pulling you whent too far

 

that sounds easy enough, but my truck will start if i try to turn it over. i mean the starter makes like 2 turns and she's running...lol....not like the old days when I could remove the center distributor wire...lol