OK I thought they were.

 

Ok, ok, I know this is an old thread, but for future reference and to caption this all up, as a automotive technician I have seen this many times. taking short trips and adding small amounts of fuel throw the algorithm off in the vehicles computer making it believe there is a higher alcohol content in the fueling system then what is actually present causing injector pulse widths to become extended (takes more alcohol then gas to get the same combustion) because of the flawed alcohol percentage level the computer is reading. Fuel composition and fuel trims need to be reset, and suggested oil change should be performed to correct this issue most of the time. Well at least here where I'm from (Southern California). If you have access to a scan tool with live data check your fuel trims and alcohol content/percentage readings to confirm. You can also take a sample of your gas to check the alcohol percentage just for good measure. Hope this helps someone in the future who encounters such issues with the p0172 in these gm Flexfuel vehicles. I've seen it in Impalas, HHR's, Silverado's, Tahoe's, and many more.

 

You are 100% correct. Sadly, my wife is the culprit here on this. If I would of bucked up in the beginning and bought the proper scan tool (Matco Maxme in my case) from the start, I could of saved alot of time and effort to fix this issue. Positive note, I've got my MaxMe now. LOL

 

My wife’s daily driver, 2011 LS w/ 70K miles, was exhibiting the same symptoms, and she also makes a lot of very short trips, about 1 mile. This thread
was the first Google hit, I think.

TLDR:
Remote, crank no start. Key, same. It eventually starts w/ some gas pedal. Runs rough, finally smoothes out. Had just filled up the night before. First time ever having trouble starting this car.

P0172 pending, no other codes, but and ECU thinks it has 46% or so ethanol even tho the fuel is tested at 11%, and there’s a leak in the fuel line, in the usual spot in front of the DS rear wheel. Guessing maybe in the vapor line too. Plastic fuel line kit will go in next week. I’m hoping OP’s fixing the fuel line was the key, but certainly not assuming that there will be nothing else to do.

Long story:
I had been watching the battery because it was the original. (I know! Ten years?!) When it ran down, I decided to just replace the battery, because no point trying to fix the car with a bad on, right? In my enthusiasm I forgot to scan for codes. Oops. Still no start, many tries not touching the throttle (doh!) still no codes of course. Car finally starts with throttle fiddling. Starts when warm, not cold. Car gets driven a bit, now the pending P0172 and the leak is detected from a gas smell.

I know the gas leak is new because I always on the alert for it, having dealt with a 2008 HHR.

Learned a lot from this thread. Of particular interest is how the car detects a fill-up and then imputes the ethanol content.

I thinks it’s plausible that the fuel line leak causes a lean condition on startup, and because the of the fillup the trim got adjusted for more ethanol than is actually in the tank, ergo, P0172. Hoping that’s the full explanation, but certainly no point exploring further when the fuel line won’t hold pressure.

Gotta wonder if OP’s short trips and ours are just a coincidence.

Car is parked until fuel line repair because of course the leak could get a lot worse quickly.

Someone pester me if I forget to follow up by the end of next week.

 

That fuel line problem maybe the source, but if it’s the pressure line, you would have a lot of fuel gushing from under the driver’s side rear tire area.

https://www.obd-codes.com/p0172

It could also just be a dirty MAF sensor.

 

A little follow up after a long delay
It typically starts just fine, it always starts fine when using the remote start.
I only find that it's myself or someone thats never been in the car that has trouble starting it with the key now. We're passing the car onto our daughter, as my wife has purchased a new car. As long as I use the remote start, always starts perfectly fine.

My wife said, its something in the way i turn the key. Dunno...

 

Could be you press the throttle pedal or hold the key to long, try right foot on the brake, and turn to key and release, it really just starts the computer to engage the starter and it adjusts the throttle for start up.

 

Must just be a tiny pinhole. Infrequent drips when running, eventually all but stops when off. Parked to slow progression of leak, pending repair tomorrow.

Throttle body and MAF sensor already cleaned. Throttle body was a bit dirty. Not mentioned previously because the cleanings had no apparent effect, but certainly not wasted effort. Should have mentioned it, sorry.

 

There is a check valve in the pump to keep fuel in the fuel rail for col starts. If there is a hole in the fuel line it cannot do it's job.
If there is a hole in the line the fuel pressure will be lower causing P0172 along with too much air getting into the vapor line through a hole there.
It is mostly the O2 sensors that calculate the alcohol. Alcohol releases oxygen when burned. The computer senses more oxygen assumes it is from alcohol burning..

Enough fractured chemistry.