You have an AUM engine, these engines are known for this code, it is also known as a "ghost code" which means the car thinks it has this error when it does not. I too have the same engine and I too have this code pop up alot, however I am starting to think I have the "ghost code" problem. Because I have changed almost everything and I mean everything related to this code.
The only way to remove the code is a ecu software update, IF it is ghost code related.
The most common places the AUM leak are..
* That big metal pipe at the back is called a charge pipe. Half way down behind the engine, the metal pipe meets a rubber hose, now the AUM engine uses a "C" clip design to meet the two pipe which commonly leaks, beat way to check is to get the car jacked up on the drivers side, remove the drivers wheel and get yourself underneath, look at the join of the rubber pipe and the charge pipe. If you have a leak you should see oil deposits around the join, also chevk that rubber pipe for splits. While your there follow that rubber pipe and it will meet whats called the "pancake pipe" check the join there then follow again you will meet the "sandwhich pipe" I think u get the idea here...
* Next you want to inspect all the rubber pipes on the top on the charge pipe, follow the pipe they go to many places, follow them all and check, remove the pipes if you have too.
* Check the "Y" shape pipe that is connected to the right hand side of your rocker cover, it connects to a "Hockey puck" type device, it commonly splits underneath so you will have to remove it.
* Check your diverter valve, make sure that is not leaking, search the forum or google how to chevk DV for leaks.
Any tubber pipe, check it, the most common sign of a leak in an area is old oil around the area, also your shudder will most probably be your TB (it was with mine as mine did the same) pull your TB off, buy some carb cleaner and give it a really good clean, search the how to section of how to clean your TB, also dnt worry about alining the TB, AUM's allin themselves.
Hope this helps
