So, I recently put in a new head gasket set I'm my 99 MC ls 3.1 a couple weeks ago. Now when my car idles the rpm's vary from 500to 2000 when idling, and I am throwing a p0171 code (system too lean) I have it narrowed down to a couple of bad vac lines, but when I went into the parts store and asked for them they looked at me like I was an idiot. I need to know the names of the vac lines before I am able to order them... one is the line that goes from the pcv valve to the plenum,then around to the back of the engine. The oher line goes from the air intake tube to a spot on the rear valve cover. Any help would be appreciated

 

Usually places like autozone won't carry the specific oem vacuum lines for your car, which is likely why they were confused.

They do sell generic pieces and connections you can use to install new lines.
The only issue I've seen so far with using aftermarket vacuum lines is that (at least on the 6th gens) GM used small solid tubing for the vacuum lines and big soft connectors and T fittings. The ones you'll usually find at a part store will be a larger soft tubing and small hard connectors/T's.

A chevy dealer should be able to order the exact parts you need as well, but a lot of the vacuum lines come as large pre-assembled sets (found this out when the PCV elbow on my old '01 LS cracked and split..had to buy the whole section for it).

 

That's what cracked on mine as well. Patched it up with some rtv for the time beimg.. guess I will be going to the dealership tomorrow
Thanks!