So temperatures here have dropped recently, and my van developed a new problem. When the engine is cold, it doesn't start normally. The starter motor cranks fine, but the engine is lazy to start. I still only have to crank once, but the engine hesitates and spins up slowly, then surges. It responds normally when I press the accelerator, but the idle RPM fluctuate up and down until I put it in gear and drive away. Once warm, the problem stops. Meanwhile, the computer throws OBD code P0172 or P0175, which is mixture too rich in Bank 1 & 2. I think that's a symptom and doesn't tell me much about the cause. It seems to be getting worse.

Has anybody experienced this before?

I plan to take a peek at the MAF sensor and make sure its clean.

2013 5.3L

 

SO like an extended cranking cold issue? Coolant temp sensor?

 

No the crank isn't extended. The engine catches right away but then hesitates a bit before coming up to idle RPM. No coolant trouble codes.

 

If you were to cycle the key an extra time before cranking, does it change anything? Cleaning the MAF seems like a good idea as well as looking for a vacuum leak. At least from the cheap seats...

 

A vacuum leak would cause a lean condition not rich.

 

maybe try a throttle body clean and then do a idle relearn. if the throttle plate is not letting enough air in do to crud build up..it may run rough for the first few seconds.

for the dtc...check the freeze frame data...what is the rpm and engine run time when the dtc sets? Is this a flex fuel vehicle?

 

It's a flex fuel vehicle. The DTC only sets during the abnormal starting. It clears itself a short time later.

 

have the flex fuel sensor reset...if its askew...reading the wrong OH% content it will set rich dtc

 

So you were right. This has been an ongoing and supremely irritating problem.

I only ever fill up with regular gasoline (max 10% eth) , but ECM always gets it totally wrong. It reads ridiculously high (70% or more), and that throws the fuel trims way out , which causes it to struggle to start, idle erratically, run rich and burn too much fuel of course (tailpipe covered in soot). So then I have to reset it, and it goes through fuel trim relearn, and then it runs perfectly for a while. Eventually, it happens all over again. It's supposed to be a flex fuel engine, specifically intended to handle variable fuel compositions. But what does it do?... The complete opposite. It craps the bed. Up yours GM.

Do you know of a permanent fix for this? I saw in the diagnostic data one of the parameters says 'flex fuel enabled' or something like that. Is it possible to program it out completely and disable it? I don't ever intend to use E85.