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Discussion Starter · #1 ·
Quick vehicle issue history:
  • Engine would shake badly when idling after long drive almost as though the car wanted to turn off and would get a strong gas smell. Would only get the gas smell when it would shake. Also noticed that the temp gauge reading would go above 210 when shaking and would drop once it stopped. This would trigger the Stabilitrak/Traction Control to come on. CEL would come on and would get P0171 code and forget the other code. Therefore, I replaced the air filter, MAF, and cleaned/relearned throttle body even replaced the gas cap and since then the Stabilitrak issue stopped.
  • Engine would still shake after long drive during idle but not as rough would get CEL for HO2S Slow Response Bank 1 Sensor 1 but did not pay attention to the temp gauge. Therefore, I replaced both upstream oxygen sensors and no more CEL for sensor.
Yesterday after about an hour of running errands I was sitting in the driveway felt the car shaking but not as rough as before and not as long. Plugged in the OBD2 reader and the STFT B1/LTFT B1 reading was high when the car would shake and noticed that temp gauge reading would go above 210 but once the shaking stopped the STFT B1/LTFT B1 reading dropped as well as the temp gauge to normal reading. Got somewhat of a gas smell by the engine other than that no smell. I have attached a video of the STFT B1/LTFT B1 readings. Plugged in the reader when I got home just for the heck of it and a P0171 along with a P0300 popped up but no CEL. Car has about 65K miles and overall engine performance is good. MPG has improved.

 

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2020 High Country
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High STFT are usually caused by a vacuum leak or a bad MAF.
Did you use a AC Delco Genuine GM MAF on the replacement one? Aftermarket ones are not reliable.
Stabiltrak warning will always come up when a check engine light activation occurs or a code is set even if CEL doesn't stay on.
Check your fuel pressure, issues after a long drive may be a sign of fuel pump loosing pressure after heating up, low fuel pressure can set a P0171 code and give a rough idle and misfire codes.
 

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If it's only one bank I wouldn't think that points to a MAF or vacuum leak.

The fact your getting a miss fire makes me lean towards fuel/spark on that bank. That would also drive your fuel trims off. Would be a good idea first to pull the plugs on that bank and see what they look like - is one wet or all carboned up? Bad injector or bad coil could be the culprit.

Also could have an exhaust leak at the mainfold or close to the front O2 sensor, polluting the exhaust stream with O2 and causing false readings and too much fuel being dumped in.

Also curious, does it idle fine at cold start, or does it miss then too? If it runs fine at cold start when the car is in open loop (ie no O2 sensor feedback being used yet) that might rule out the plugs/coils/injectors.
 

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I didn't notice the bank one, good catch.
Possible vacuum leak on bank one side of manifold affecting that side ?
Any add on stuff like a catch can?
No response yet on non GM parts.
 

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Discussion Starter · #5 ·
I didn't notice the bank one, good catch.
Possible vacuum leak on bank one side of manifold affecting that side ?
Any add on stuff like a catch can?
No response yet on non GM parts.
Sorry for the late response. The MAF was GM. What range should the fuel pressure be?
 
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