During the process of removing the grommet with red ring on the intake manifold, I later found out that the back rubber end has been broken off and fell into the cavity of the intake manifold plenum and so on.The broken piece is the hard plastic black circular ring . I try to look in the intake manifold via the throttle body and saw there is a cavity near the end of the other end of intake. I could not see the missing black plastic end. See enclosed photos. The black plastic ring must have fallen into the cavity into the plenum that makes it nearly impossible to be fished out.

My question is: What effect does the small hard plastic end of the grommet do to the engine. Will it cause any harm?
There must be other people on the forum who broke the pieces while replacing them. Who are those people and what were heir experiences with it.

 

I would disassemble as much as necessary to get it out

 

Not clear exactly what part of the grommet you are referring to. Of course it is a risk if you let the engine eat it, but it might have already done so. An engine can eat a small piece of plastic without too much trouble but metal is a different story. Pics of what is left might help.

 

You may be able to see it through the throttle body if you open it or remove it and shine a flashlight in there from that end - did you try that? that would be my first "go to"

Did it break into bits or all in one bit?

I wouldn't worry about it too too much - the motor would eat it up. The bigger issue would be it blocking something. Even that not a huge huge deal.