2010 Tahoe/Erratic idle (no codes detected)

[Peppy]

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..

The truck is turned off while using smoke. The smoke gets pushed through the system using a smoke machine and if there are any openings down the line the smoke will seep through.

 

[mikez71]

DOH!.. Guess I should have looked it up..
Thanks for the explanation!

 

[Gearz]

A MAF sensor can be bad even though you cleaned it, also what did you clean it with?vI hope not carb or brake cleaner. You need to monitor fuel trims also and see if you have a rich or lean condition. Sorry did you say mileage? Like it was mentioned earlier possibly Pre-Oxygen sensors not post. ( before cat converters ) What is your coolant sensor say for temperature?

 

[Peppy]

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

I agree it can get expensive throwing parts it for sure. How accurate is the scanner if there are no Engine check light on? I'm a bit confused about that because scanner will show codes, but I don't know if I should start replacing parts based off that and I show codes on all 02 sensors witch I think is very odd. When I ran live data, it seems to be within tolerance and fluctuating but that is expected. My readings were...(B1 S1 - 520Mv), (B1 S2 - 740Mv,) (B2 S1 - 500Mv) B2 S2 - 695Mv) I also did a fuel pressure check, and that was within tolerance at 60psi. I like to learn and figure things out on my own, but if I can't figure it out then I will have to take it to a certified mechanic and ask him to scan if for me.

 

[Gearz]

A scan tool is not a code reader. The scan tool like the Tech 2 enables you to not only read and clear codes but see live data and with the add of a GM manual you are able to see what the data is reading and find out what is normal and not normal. Did you also do a compression test to make sure all cylinders are firing? If you don't have the tools and the experience then you need to find a qualified technician to find the cause. There is much more to cars than just throwing parts at them as you said. I'm a retired GM technicians and I don't on a scan tool any longer at my age and it's hard to find someone you can trust to diagnose your car correctly. I know the dealership's rates are crazy but sometime it's the only way to fix it right. Good luck your gonna need it.

 

[Doubeleive]

I agree it can get expensive throwing parts it for sure. How accurate is the scanner if there are no Engine check light on? I'm a bit confused about that because scanner will show codes, but I don't know if I should start replacing parts based off that and I show codes on all 02 sensors witch I think is very odd. When I ran live data, it seems to be within tolerance and fluctuating but that is expected. My readings were...(B1 S1 - 520Mv), (B1 S2 - 740Mv,) (B2 S1 - 500Mv) B2 S2 - 695Mv) I also did a fuel pressure check, and that was within tolerance at 60psi. I like to learn and figure things out on my own, but if I can't figure it out then I will have to take it to a certified mechanic and ask him to scan if for me.

you probably would want to graph the 02 sensors I believe the front should both be about the same and rear should be about the same
the graph would show if one was dropping out under a load or something. I am not familiar with the exact specs @Fless probably has a better idea

 

[Fless]

It would be interesting to see what the short- and long-term fuel trim values look like, both at idle and at 1800rpm or so.

It looks like your Foxwell scanner can graph, so graphs of the upstream O2 sensor activity might also be helpful.

If you can read the live data at a hot idle, what is the MAF reporting in g/sec? This might be difficult if the idle is moving too much, but it should be close to the engine displacement.

With the issue being mostly at idle, a vacuum leak is in the mix. Fuel trims at the different rpms might verify that as the cause. I'd be doing a very close inspection of the vacuum lines for cracks, and of the intake pipe between the MAF and the throttle body to make sure there are no leaks or cracks. What's the condition of the air filter?

Another thing that can cause this is a dirty or defective idle air control valve on the throttle body.

 

[Peppy]

A MAF sensor can be bad even though you cleaned it, also what did you clean it with?vI hope not carb or brake cleaner. You need to monitor fuel trims also and see if you have a rich or lean condition. Sorry did you say mileage? Like it was mentioned earlier possibly Pre-Oxygen sensors not post. ( before cat converters ) What is your coolant sensor say for temperature?

No not carb cleaner! I used MAF cleaner. I figure I would have a code or engine check light on if the MAF was not functioning. I do not monitor the fuel trims and no I didn't check the coolant sensor. I didn't even think about checking those areas, but I will look into now. there is 179k miles. I might send it to a certified mechanic to get more in dept answers that I may not be asking the right questions.

 

[mikez71]

Similar issue here? https://www.tahoeyukonforum.com/threads/tps-issue-and-dealer.151816/
No solution yet..

Is there TPS calibration that needs to be performed? There is mention of one here..

How to perform a GM throttle body relearn procedure

Learn how to do a GM throttle body relearn to establish a new baseline idle after replacing or disconnecting the throttle body.

ricksfreeautorepairadvice.com

1) Start the engine and let it idle in park for 3 minutes. During that period the idle may be higher idle than normal.
2) After 3 minutes, turn the engine off and leave it off for 60- seconds.
3) Start the engine again and let it idle in park for 3 minutes one more time. During these run periods, you may see a check engine light. Scan for codes and if you get throttle body-related codes, clear them.
4) If the idle speed is still off, drive the vehicle at speeds above 44 mph and operate several acceleration and deceleration cycles. Then repeat step #3 one last time.

NVM just noticed you said you relearned it with a scanner, I think there's another simlar thread I was going to paste that into..

 

[H2oboyz]

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.

Have you tried resetting the throttle position sensor?