2010 Tahoe/Erratic idle (no codes detected)

[Peppy]

I have a 2010 Tahoe LT with 179xxxx miles that I purchased 3 month ago. My idle is erratic and sometimes stalls when I'm at a stop. It drives fine when I'm on the gas peddle driving it's just when I'm at a stop it goes crazy and sometimes stalls out. I will even put it in neutral while driving it and you can see the idle going crazy and sometime stalls out. I have no engine check light on! I hooked it up to an OBD 2 reader anyways and nothing but when I ran a scan on the engine there are all kinds of codes that pop up from HVAC, o2 sensors, and a few others I can't remember off hand. I'm not very experienced with the scanner but why is the OBD reader not reading anything but the scanner is reading all kinds of codes. I'm using a Foxwell nt501 scanner made for GM trucks

What I have done so far:
- changed out the spark plugs and wires.
- changed out the body throttle and (relearned it to the ECM with a scanner)
- checked the vacuum system by pushing smoke through the system with a smoke machine and I sprayed carb cleaner around the hoses and found nothing.
- changed out the exhaust manifold gasket only because I had to replace the oil pressure sensor
- I reset the Alcohol fuel content because it was showing %17

I'm thinking of replacing the VVT next. I want to change out the water pump anyways just because I don't know if it was ever changed out.

 

[Miami-Dade]

@Peppy Moved you here from 2015 Section.
Welcome from Miami&Queens NY!

 

[Doubeleive]

I have a 2010 Tahoe LT with 179xxxx miles that I purchased 3 month ago. My idle is erratic and sometimes stalls when I'm at a stop. It drives fine when I'm on the gas peddle driving it's just when I'm at a stop it goes crazy and sometimes stalls out. I will even put it in neutral while driving it and you can see the idle going crazy and sometime stalls out. I have no engine check light on! I hooked it up to an OBD 2 reader anyways and nothing but when I ran a scan on the engine there are all kinds of codes that pop up from HVAC, o2 sensors, and a few others I can't remember off hand. I'm not very experienced with the scanner but why is the OBD reader not reading anything but the scanner is reading all kinds of codes. I'm using a Foxwell nt501 scanner made for GM trucks

What I have done so far:
- changed out the spark plugs and wires.
- changed out the body throttle and (relearned it to the ECM with a scanner)
- checked the vacuum system by pushing smoke through the system with a smoke machine and I sprayed carb cleaner around the hoses and found nothing.
- changed out the exhaust manifold gasket only because I had to replace the oil pressure sensor
- I reset the Alcohol fuel content because it was showing %17

I'm thinking of replacing the VVT next. I want to change out the water pump anyways just because I don't know if it was ever changed out.

the 02 sensors are a "sign" and you may want to check fuel pressure and clean the intake and maf

 

[Foggy]

To add: the oxygen sensors themselves could just be worn out..
Usually anything over 100k and they sure "need" to be replaced for
best performance.. Don't go with cheapo ones. Get GM or Delphi

 

[mikez71]

Leaking intake manifold gaskets?
You checked vacuum, but did you spray the base of intake manifold?

Definitely make sure your O2's are good.
Usually if you have a code for those, you would have a check engine light...

When you say idle goes crazy, do you mean it jumps all over the place?
Or is it only stumbling/stalling?

Also try to record the actual codes.
FWIW I regularly see 10+% ethanol on regular gas..

 

[Peppy]

the 02 sensors are a "sign" and you may want to check fuel pressure and clean the intake and maf

Thanks for the response. I forgot the mention in my original post that I did clean the MAF and intake. For my truck to run that bad I figured the engine check light would go on. I'm new the scanner world so I don't know how accurate the scanner is when the truck isn't throwing any codes. Should I trust it and change out the 02 sensors? I'm using a Foxwell nt501 elite

 

[Peppy]

Leaking intake manifold gaskets?
You checked vacuum, but did you spray the base of intake manifold?

Definitely make sure your O2's are good.
Usually if you have a code for those, you would have a check engine light...

When you say idle goes crazy, do you mean it jumps all over the place?
Or is it only stumbling/stalling?

Also try to record the actual codes.
FWIW I regularly see 10+% ethanol on regular gas..

Thanks for your response.

I figured putting smoke through the vacuum system would show if the intake is leaking, plus I did spray the base of the intake manifold, and everything is fine. I'm planning to replace all 02 sensors as soon as they come in.

Crazy meaning.. RMP's jump to about 1500 to 2k and then drops and goes back up and drops again fast and sometimes stalls out.

I need to figure out how to record the actual codes.

 

[Fless]

A review of the O2 sensor activity -- both upstream and downstream -- would possibly guide you a bit closer to the cause. Evaluating fuel trims might also help.

You may want to have someone a little more knowledgeable with diagnostics take a look at it.

 

[Doubeleive]

Thanks for the response. I forgot the mention in my original post that I did clean the MAF and intake. For my truck to run that bad I figured the engine check light would go on. I'm new the scanner world so I don't know how accurate the scanner is when the truck isn't throwing any codes. Should I trust it and change out the 02 sensors? I'm using a Foxwell nt501 elite

It would be wise to monitor what the maf and 02 sensors are showing and check the fuel pressure, you can use the scanner rule things in or out instead of just throwing parts at it

 

[mikez71]

I figured putting smoke through the vacuum system would show if the intake is leaking, plus I did spray the base of the intake manifold, and everything is fine.

I'm not sure if smoke in the vacuum system would show intake leaks. ?
I figure the intake is drawing air in (constant vacuum?) and would just suck additional air in with the smoke.?
I've never done it.. someone feel free to enlighten me..

Regardless, it sounds like you checked it all out..

X3 on checking sensor data. Also getting the actual codes usually points you in a direction..