Ok, so the cobalt has not been working properly lately.
The problem is, the bypass valve seems to be sticking or it can't handle the boost so it makes the turbo flutter and can only hold 15 PSI. The car has a stage 1 GM tune.

He tried replacing some bypass valve piece but that didn't do anything. He noticed this problem months ago when he turned on the A/C 10 second after he turned the car on from a cold start and then he started going, the bypass valve would get stuck and he would have turbo flutter. If he waits to turn on the A/C till he drives a mile then the car is fine. Anyone have these problems?

I'll update this post once I get more info tomorrow, and maybe a video of cold start and a short drive.

 

Most sure to check the lower TMAP sensor. It could be rubbing on the AC line.

 

Who turns the AC on that early? Driving 1 mile helps before turning it on helps? Than just do that. Hope "he" isn't just turning on the car and giving er.

Turn the key to the on position. Let the fuel pump do it's thing and pressurize. Wait till all the lights and chimes have stop beeping. Start the car. Let it get out of cat warm up high idle. Than drive easy till it's up to operating temperature. After that than go ahead and use your AC.

 

also take a look at your vacuum canister under your intake manifold. if that cracked it will cause flutter. it happened to me.

 

He always lets is pressurize every cold start.

 

I am having a very similar problem on my balt. I replaced the BPV but that didn't really change a damn thing. I have replaced the vac canister as well as the BPV control solenoid. I have replaced both TMAP sensors and resoldered the connections to the lower TMAP. It does seem to improve when the car is warm but not always. AC on definitely worsenes the problem. I have considered going back to the stock BPV but I don't have much hope as I am sick of replacing parts with no improvement. I always get codes for MAF, TMAP voltage out of range etc. At least I am not getting flutter anymore but the damn thing still runs like hell for the first 5 min after startup. BTW I think it't ridiculous to have to baby a modern car at startup. EFI and DI cars should be able to start and run immediately. We aren't talking about carburators anymore. I am old enough to remember that **** and I hate the idea that I have to treat this car like it is carburated. End rant.

 

Well the big difference is that you have an entire turbo setup to worry about too. That's why the problem is so complex.

Boost Leak
Wrong 0-ring on Tmap
dirty sensors
wire rubbing on AC line.
TMAP not seating lower charge pipe correctly
Leaving surge tank
aftermarket BPV
aftermarket intake