I've had a problem with my 2008 Cobalt SS for years and I have never been able to solve it. Everytime it starts acting up, I bring it into a shop and it doesn't happen when they have it. The problem only happens in the summer when the outside temp it above 70°. This morning it was particularly bad on the way into work. I was able to get logging turned on in my Torque app and logged the entire drive into work.

The info that I have: Car has the Stage 1 upgrade and a Hahn Catback exhaust. Car shakes violently when the issue is happening. Boost generally won't go over 0 but this morning it wouldn't go above 10psi in vaccum. Engine Codes P0101, P0106, P0300-P0304. I've attached logs from Torque on a good day going up to the next interstate exit and back. Bad Trip is this morning and the issue was happening throughout the entire log. I hope that the Torque log has the info needed. Thanks!

edit: I don't have much knowledge on what the logs actually mean, but I imagine they are not supposed to show the same data for twenty seconds in a row. I would assume that is going to be the problem.

Freeze Frame Data:
Freeze frame information:
------------------
Fuel Trim Bank 1 Long Term = -10.938 %
Intake Manifold Pressure = 4.786 psi
Engine RPM = 823.75 rpm
Speed (OBD) = 0 km/h
Timing Advance = -4 °
Intake Air Temperature = 45 °C
Mass Air Flow Rate = 4.8 g/s
Throttle Position(Manifold) = 21.176 %
Run time since engine start = 4 s
Fuel Rail Pressure = 587.403 psi
Fuel Level (From Engine ECU) = 22.745 %
Barometric pressure (from vehicle) = 14.069 psi
Voltage (Control Module) = 14.206 V
Engine Load(Absolute) = 29.412 %
Commanded Equivalence Ratio(lambda) = 1
Relative Throttle Position = 6.667 %
Ambient air temp = 18 °C
Absolute Throttle Position B = 21.569 %
Accelerator PedalPosition D = 20.392 %
Accelerator PedalPosition E = 20 %

End of report.

 

My first guess with a P0101 is a boost leak. Most likely shows up when warm out. You will need to cheack all connections in the intake pipe, intercooler piping and the intercooler itself.

Next i would check wiring to the MAF and MAP sensor. I would also clean both map sensors.

You may want to build a boost leak tester. It could be leaking around the bottom MAP sensor if the O ring is the wrong one.

Notice how you LTFT is -10% With Minimal mods your LTFT is pretty far off.

 

Update: I've cleaned and replaced the MAF and MAP sensors in the past. Smoke test at a repair shop found no leaks. I found out about the wrong o-rings a couple years ago and have the correct ones from CED. Repair shop said one of the sensors was slightly loose but said it's unlikely it was the problem. One thing that happened yesterday was I experienced the problem on the 20 mile drive into work. I stopped at a shop, they couldn't look at it, started the car back up and the problem was gone.

If the problem was the loose sensor, where should the LTFT value end up? I found other places that the connections on the Stage 1 sensors may be bad and to solder them properly so I might try that next. I also found a TSB saying the nuts on the waste gate actuator could be loose and cause the problem.

 

Someone correct if I'm wrong but a smoke test won't do ****. It's not under pressure so it won't show a proper leak. P0101 is a boost leak 90℅ of the time. If you are still getting the code you need a boost leak tester than you can apply 15-20 psi to and really test. Has the bumper been pulled off and the intercooler inspected?

 

Correct, smoke will find it's way out of a normal hole, but if the charge piping is to be tested it needs pressure. I'd test the piping as well as the following, but, we need more info on your car... P0101, MAF performance. do you have an oiled air filter? Over oiling can coat the MAF and skew the data, causing issues. If not, clean the MAF sensor with the proper MAF cleaner ($5 at walmart or local store that sells auto stuff) and report back. Also wiggle the MAF sensor wire while watching your TORQ app on your phone and see if codes pop up.

Stage 1 on the LNFs, installed by a dealer, are known to have wiring issues. Some dealer techs don't know how to solder worth a damn, so I've read. Though they don't touch your MAF, they do fiddle with the MAP sensors, which brings me to...

P0106, MAP sensor code. Both P0101 and P0106 are 'circuit/range performance' codes which is a fancy way of saying the data they expect to gather is outside of the norm. I'd check that lower TMAP in the charge piping as well as the MAP in the manifold (both fiddled with during Stage 1 install) and check for wiring issues.

I'd bet a 6-pack of my favorite brew that the wires to those sensors are to blame. An incorrect MAP sensor reading can throw a MAF code. The car goes "hey wow I have air coming to the throttle body at Temp X and it's under Y PSI of pressure, that must mean that Z amount of air entered the car"

So the 3 work in tandem... MAF to accurately measure air pre-turbo, TMAP after the intercooler (the T is for temp and this is the IAT2 if you've seen that term thrown around) to measure temp and pressure, and the secondary MAP that's in the intake mani. If they all don't work together to accurately calculate the amount of air pre and post-turbo, your car will lose it's **** and not know which one is lying... is the MAP off and the turbo didn't make boost? is the MAF off and didn't know how much air came in?

Check those 3 sensors, do a boost leak test then report back. I followed this guide. Good luck.

 

I just talked to the shop. They have their smoke machine hooked up to a 50psi compressor. The guy put enough pressure into it that it popped one of the charge pipes off. He was adamant that it is not a boost leak.

I do not have an oiled air filter. The shop said they found one of the screws was a bit loose on one of the MAP sensors. After that was tightened down, my LTFT has been a lot better sitting at around -5%. I've done some more reading on LTFT and that makes sense if the sensor was leaking. I have not thrown a P0101 or P0106 code since the shop had it on Friday but I have thrown a P0420 code twice over the weekend. The tech at the shop said that is most likely the cause of all my problems.

My plan now is to go get the cat tested to see if it's clogged. If it is, I'll get that resolved. The next step would be to solder the MAP connections. Temps are back up in the 90°s the mid week so hopefully the problem doesn't come back.

 

First of all don't put more than 15-20psi through the system. You will do damage to your engine. Surprised the charge pipe didn't explode

A P0420 code is usually due to an aftermarket downpipe. I have gutted my second cat and I have only seen this code once in 3 years. Usually when people get tuned they turn off the P0420 code because it does no change the performance of the car. Again, 420 does not affect performance.

If you fuel trims are back at -5% then you are within acceptable range for driving.

So are you on the stock downpipe and cat or aftermarket? If you don't have emissions testing then gut the second second cat out, I did it by removing the exhaust from the downpipe and shoving a metal tube through the cat. Then you would still need a tune to get rid of the P0420

 

I didn't ask specifically what pressure they ran through the car. It was the office guy that said it was hooked up to a 50psi compressor. The tech said one of the charge pipes popped off. I never got an exact number they tested it at but it was enough to pop a pipe off.

My car is entirely stock except for the Stage 1 and the Hahn Catback exhaust. I just grabbed lunch and pulled codes again to find that the P0420 code is only pending. That is the only code coming up on the scan but the engine light is on. I have always thought that a pending code would not produce a check engine light. Is that not correct?