What year car?
How many miles?
Any previous issues or problems?
Eliminate the easy things.
Check the oil for level and any contamination.
Check the coolant for level and any contamination. Only when cold and with the filler / overflow tank the highest point in the cooling system
Pull the charge tube at the turbo and check for oil. Potential PCV valve issue.
Verify that all the charge tube clamps are tight, ideally replace the factory clamps with T clamps. See many posts on this issue.
Visually inspect the intercooler to verify that there are no failures there.
Visually inspect the vacuum hoses and connertors to make sure they are sound and connected. Pay particular attention to the connection on the air cleaner as many have been broken when servicing the air filter.
Put a reader on the OBD port and check for codes. There can be codes that do not result in a CEL that might indicate what the issue is.
Visually inspect the throttle valve for condition and cleanliness.
If you have the GMPP tune, check to make sure the connectors are soldered and not crimped.
had a bad thermostat that was recently replaced and the coolant was flushed.
Changed spark plugs and installed phenolic spacer a few months ago (Oct?)
I did back out of a steep driveway a few weeks ago and heard a heart-dropping metal clang as the front dropped off the dip onto the road. it sounded really bad but I didn't see any damage to the intercooler.
-Oil was changed in Sept or Oct but I can check the level and consistency.
-Coolant should be good as it was changed 2 weeks ago
-The charge tube is the plastic pipe that connects the intercooler to the turbo, right? I'll check for oil inside. If that's the correct pipe then the previous owner installed T clamps as it's got 2 on it right now.
-It's hard to inspect the intercooler as it's so low to the ground and under the hood hinge. WHat should I be looking for? I don't see it bulging, but I don't know where that would be or what it'd look like. There's been some damage to the heat dispersal fins since I bought it, but nothing i can see out of the ordinary. I had the car on a lift 2 weeks ago and gave the whole undercarriage a once-over but didn't see anything concerning (besides a leaking rear differential).
-What are the vacuum hoses? Are they located on the turbo, the manifold, or?
-I'll check the air box.
I havent been able to get my OBDII adapter working. it stopped showing up as a bluetooth device. This is more my expertise and I haven't spent much time troubleshooting. As of 2 weeks ago it was code-free, but who knows what's happened since then.
-will check throttle valve as well
-i have trifecta budget tune using stock MAPs
As always, thanks for the responses. cars are not my expertise, but i love learning (and hating paying others)