braveheartwallace
TYF Newbie
- Joined
- Dec 21, 2017
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Wanted to post this here to get some of y’all’s thoughts on what may be going on.
This morning where I am in New Mexico it was a cool 9˚. I went to start my Hybrid Tahoe (6.0L vortec) and it had this incredibly rough idle as recorded in the following youtube videos:
Initial start:
A couple more attempts after engine repeatedly “stalling”:
Running normal after idling for a few minutes:
One thing to note about this hybrid model is that the computer cranks the engine for up to 10 seconds at a time from the drive shaft via the hybrid transmission, similar to bump/roll starting a manual car. There is no traditional starter like on non hybrid models.
In the first two videos you can see me start the car after it stalls/shuts down on its own. I am unsure if the engine actually fired or not. The engine may not have actually been running and just constantly being turned over by the hybrid’s electric motor.
At the end of the second video where I say, “I’m going to end the recording to check that engine light” the reported codes were:
P1400 - Manifold Differential Pressure Sensor
P0506 - Idle Speed Control System RPM Lower than Expected
P0300 - Random cylinder misfire detected
P0011 - Intake Camshaft Position System Performance (Camshaft Position System replaced less than 2k miles ago, code hasn’t resurfaced since then.)
I cleared the codes and restarted the engine smoothly. Drove for a couple hours with no apparent problems and check engine light never came back on.
Anyways, my theory is the roughness was the result of the computer managing the engine in an “open-loop” without any data input from the freezing-cold downstream O2 sensors resulting in improper fuel/air metering. Once it had warmed up enough, I think it switched to a “closed-loop” where all sensors were sending data thus allowing it to meter fuel/air properly and idle smoothly.
The car has been in these cold conditions before but never has ran this rough on a cold start. Any and all thoughts are welcome!
Edit: MAF sensor and throttle body were cleaned at same time when the camshaft position system was replaced.
This morning where I am in New Mexico it was a cool 9˚. I went to start my Hybrid Tahoe (6.0L vortec) and it had this incredibly rough idle as recorded in the following youtube videos:
Initial start:
A couple more attempts after engine repeatedly “stalling”:
Running normal after idling for a few minutes:
One thing to note about this hybrid model is that the computer cranks the engine for up to 10 seconds at a time from the drive shaft via the hybrid transmission, similar to bump/roll starting a manual car. There is no traditional starter like on non hybrid models.
In the first two videos you can see me start the car after it stalls/shuts down on its own. I am unsure if the engine actually fired or not. The engine may not have actually been running and just constantly being turned over by the hybrid’s electric motor.
At the end of the second video where I say, “I’m going to end the recording to check that engine light” the reported codes were:
P1400 - Manifold Differential Pressure Sensor
P0506 - Idle Speed Control System RPM Lower than Expected
P0300 - Random cylinder misfire detected
P0011 - Intake Camshaft Position System Performance (Camshaft Position System replaced less than 2k miles ago, code hasn’t resurfaced since then.)
I cleared the codes and restarted the engine smoothly. Drove for a couple hours with no apparent problems and check engine light never came back on.
Anyways, my theory is the roughness was the result of the computer managing the engine in an “open-loop” without any data input from the freezing-cold downstream O2 sensors resulting in improper fuel/air metering. Once it had warmed up enough, I think it switched to a “closed-loop” where all sensors were sending data thus allowing it to meter fuel/air properly and idle smoothly.
The car has been in these cold conditions before but never has ran this rough on a cold start. Any and all thoughts are welcome!
Edit: MAF sensor and throttle body were cleaned at same time when the camshaft position system was replaced.
Last edited:
