Chasing a rough idle?

Fless said:

Use a scanner on it that can count individual cylinder misfires to see what the counts look like.

The IAC (you know, Idle Air Control) on the throttle body may need to be cleaned or replaced.

The LTFTs are a bit high -- it's learned to take away fuel so you may want to check the operating fuel pressure to see if it's high.

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j91z28d1 said:

trims removing 10% fuel from each side is a signs it's bit happy.

can your scanner read alcohol percentage?


intake leaks? exhaust leaks? missing any exhaust manifold to head bolts? they are common to be missing.


how does one do a fuel trim reset? I've seen it posted but don't know how this commonly done?

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Fless said:

The reset for alcohol percentage is just that, and I believe it will also reset the LTFTs. Now I'm not sure if there is a reset just for the LTFTs, but that could vary by year and fuel system. I would think it would need to be separate, as you may not want to do both at the same time.

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j91z28d1 said:

yeah. reset both at the same time would be good, just to make sure. Basically my thought is if you can get it running without any correction going on. everything at zero and then unplug the o2 so it stays there while running. if it runs better then it's correcting incorrectly. like pulling fuel based off leaks. then you'd atleast have a place to start. if it runs even worse, then that could mean a injector is stuck open or something making it rich. followed up by checking the plugs to confirm rich or lean running badly. it's crazy how both can kinda feel the same sometimes.


but as it is with the ecm removing a bunch of fuel, we don't know if that's helping or hurting.

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2009TahoeLT said:

I did also go through all the injectors in my scanner and they all open and close. Started running rougher when I closed them. I’ll try and see if I can reset both and unplug o2 and see what happens and what readings I get. So from the readings I mentioned it does look like it’s removing fuel? I’m not sure what the normal range is.

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j91z28d1 said:

yeah. reset both at the same time would be good, just to make sure. Basically my thought is if you can get it running without any correction going on. everything at zero and then unplug the o2 so it stays there while running. if it runs better then it's correcting incorrectly. like pulling fuel based off leaks. then you'd atleast have a place to start. if it runs even worse, then that could mean a injector is stuck open or something making it rich. followed up by checking the plugs to confirm rich or lean running badly. it's crazy how both can kinda feel the same sometimes.


but as it is with the ecm removing a bunch of fuel, we don't know if that's helping or hurting.

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Fless said:

What's different in the captures? RPM? Can you get these values with it showing if fuel control (closed loop) is on, and the RPM at the time?

What is the MAF reporting in g/sec at hot idle? And what's the corresponding idle speed?

Click to expand...

Fless said:

What's different in the captures? RPM? Can you get these values with it showing if fuel control (closed loop) is on, and the RPM at the time?

What is the MAF reporting in g/sec at hot idle? And what's the corresponding idle speed?

Click to expand...

Fless said:

What's different in the captures? RPM? Can you get these values with it showing if fuel control (closed loop) is on, and the RPM at the time?

What is the MAF reporting in g/sec at hot idle? And what's the corresponding idle speed?

Click to expand...