So I have a 2009 turbocharged Cobalt SS and I have this problem where is sometimes when I start it up it doesn't give me the right boost pressure. For example when this case scenario happens it will idle in -20 like it should but no matter how much gas I give it it only gets up to 5 PSI in boost, its tuned so it should be getting 22 pis boost. Other times that works perfectly fine and runs as it should but other times it will do that problem and it all depends on if it starts up correctly or not it never changes once the car has decided if the case scenario will happen or not on Startup. I'm thinking it's the bypass valve getting stuck on carbon buildup or something but I'm not completely sure and there's no leaks in the tubes either. What could be the problem?

 

Well first let me say I’m not all to familiar with these cars as I’ve only had mine for a few months but does your message board in your car (under your rpm gauge) say: Engine power reduced? If it’s tuned the ‘learn down mode’ has to be disabled

 

No it does not say that, sometimes if i drive it yoo long with this problem happening an engine code will go off saying something like there's a boost leak somewhere even though there's not

 

When mine had a boost leak if i dogged it then it wouldn’t make boost after that til I turned the car back off then back on, have you checked you MAF?

 

You have a boost leak and most likely pending maf code because of it.

 

No i havent byt idk how that could be the problem

 

have you done a boost leak test? properly? If you have a boost leak, ur ecu will see that the amount of air the maf sees coming in is not making it to the engine, so it will throw a maf code, or pending code that may not show up for a while, will make ur car run really rich and wont let it boost past 5 psi, that's exactly how it works. so, make sure u have properly checked with a tester, and check for codes, even if engine light is not on.

 

The only reason i dont think its that is because its very situational, some days whn i start it ill have to restart it so many times till it wrks right amd other days its first start and its fine. Thats what makes me think the little valve or turbo bypass valve may have corrosion that may be stopping it from opening and closing properly, keeping it open sometimes letting the boost out there for creating only 5psi boost

 

hey man, I had the same crap happen. would be driving around, boosting, nothing, next day be driving down the road all nice, boom, maf code and cant boost. reset it, all is good. then again out of nowhere a few days later. figured out in the end it was meth dripping down from intake manifold onto my maf sensor.

 

If the car has STG1 sensors swap the MAPs