I used to have the same issue and it was from my intake setup. M car/MAF hated anything but the stock intake system with the stock intake filter, I could get rid of the program by just swapping out filters. I beret your having the same issue, have you tried going back to a stock intake (sorry didn't even read if you changed)?

 

At the risk of jinxing myself and my car, I've decided to post an update just to let those who may be following all the GMTU boost issues and potential solutions the current status of my turbo boost saga.

Shortly after my 23 Sep update, I experienced numerous no-boost/limp problems (daily and sometimes multiple times a day). I had been focusing so much on the lower MAP sensor-related issues and everybody else's boost problems that I forgot I never checked the upper MAP sensor wiring. So, rather than setting the car on fire, I decided to check the wiring and found this. The crimp connectors didn't looked that great, and the sensor 5V source wire had TWO crimp connectors installed for whatever reason. Since soldering the wires on 27 Sep, I haven't had a boost problem in over 400 miles. I checked sensor itself while I was at it, and found the sensor to be clean and dry (no oil film). I'm still holding my breath during every trip...

 

glad you got it figured out. Hopefully that will be the end of your troubles and you can just enjoy the ride.

 

Well to update my running issue, knock on wood, it has been running perfectly, must of been a airleak at the sensor. On a side note last night the wife told me her esc, brake fluid level and abs light all come on at the same time, but not every drive cycle. Now to research and fix that.

 

Just past 1000 miles without a boost problem since cutting out those nasty upper MAP sensor crimp connectors and soldering the wires. Whoooooooo Hoooooooooooo!!!

 

I had the problem,no power,missing,very low vac. Up stream 02 fixed the problem! It was an off and on problem with many codes, the 02 was not heating all the time.

 

Thanks to all for the help. Been lurking and researching my 2008 HHR SS w/stage kit intermittent boost problem for a year or so. Took to the dealer a few times but never left it for them since they were backed up for at least 3 days or could not help unless the code had set. Once the car became the wife's main ride, the car missed me and I her, it had the stutter problem more often.
1. Installed new air filter; 2. cleaned air cleaner MAF; 3. soldered and cleaned upper boost sensor, was slightly oily, access very easy; 4. soldered, extended wires and cleaned lower boost sensor, was very clean, access very hard. As the picture shows, it seems the lower sensor crimp splices were not installed reliably by the dealer. Most likely due to accessibility issues during the install of the crimps? Took for a test drive and got over 21lbs of boost! Since the car rarely stuttered for me had to wait for the wife's report. Happy to say it has not stuttered yet.

 

Failed crimp joints speak well for doing a solder and heat-shrink fix. Glad you got it found and fixed.

 

Glad a came across this thread while trolling along the forum. Mine is in the shop right now (which I won't explain here ... too much detail) but the tech is putting in a new bottom TMAP sensor because the idiot that installed it cut (dremeled) off the bolt flange and it was installed and held in with pipe clamps! (which means it has to be turned 90 degrees from where it should sit). He also told me he was going to solder my harness connections for me, which is exactly what seems to be the cause and fix listed here. Love this forum.

 

Yep. Over 5000 miles now without a boost problem since I cut out those nasty, poorly-installed crimp connectors and soldered the wires. The fix got me through the winter unscathed and, more important, through the Polar Vortex without missing a beat. :-)