Rough Idle/Misfire 00' LS V8

[allblackls]

Hello, I have had my Ls for close to 4 years now, all of a sudden it starts to misfire at random and my acceleration gets slow but it would only do it after driving for a about 20 minutes. Now it has a very rough idle but when accelerating its smooths out but is still sluggish. I have replaced coils but still the same thing. I do have a check engine light that i was told gives code P0171 & P0174 i took it in for a second look at another shop and now he says my 7th cylinder is clogged and i need a whole new engine.. is anyone familiar with this on the V8 before i spill for a new engine

 

[joegr]

Well, you need a better shop, or you heard wrong. There's no such thing as a clogged cylinder. You could have a clogged exhaust. You could have a clog in the intake (really only if it was recently worked on). Neither of those things would call for an engine replacement.

Take it somewhere for a correct diagnosis. There are lots of relatively inexpensive things that could cause your symptoms. The worst case would be jumped exhaust timing, but even than is fixable (usually). In the best case, one of the connectors to a fuel injector (#7?) has popped off.