source of rough idle and interpretation of live data

[oldschoolby]

I have been having a problem with a rough idle and after trying various repairs, have been unable to resolve the issue. I have thoroughly cleaned the throttle body, replaced the MAP sensor, replaced the coolant temperature sensor, replaced belt tensioner, replaced spark plugs, replaced motor mounts, replaced battery, replaced air filter, and performed a smoke test to check for vacuum leaks. I did get a po420 which pointed to the catalytic converter which I checked and cleared the code after failing to find any issue with the converter. I recorded live data with my scanner and found issues with the short term fuel trim and ignition timing information. If anyone has experience in interpreting scan data and determining possible solutions for data outside normal parameters, please remind the video link below and let me know what you think. Do I have a vacuum problem or more serious internal engine problem?

2004 Trailblazer LS EXT 4.2 I6

IMG_2024.MOV

MOV File

1drv.ms

 

[Mooseman]

When you cleaned the throttle body, did you disconnect the battery or pull fuses 10 & 28 for at least 30 minutes?

 

[oldschoolby]

I disconnected the battery for at least 1 hour. What is your opinion of the live data?

 

[mrrsm]

Great Video for Live Data Capture (except for the radio-TV in the background covering the sound of the Engine at Idle). Sometimes, a Badly Worn Serpentine Belt, a Bad Idler Pulley or Bad Alternator Bearings and/or a Failing Belt Tensioner can cause this Engine to shudder in response whenever the A/C MAG-Clutch Engages and Dis-Engages. Your Engine Idling at slightly higher than 600 RPM is still pretty nominal, prior to your engaging the HVAC system.

Try removing the Serpentine Belt and then Start-Run the engine momentarily at Idle and raise it up to around 1,500 RPM while listening for anything unusual. Then Shut Off the Motor and spin the Idler Pulley and listen for anything untoward or showing any excessive resistance. Same thing with spinning the Alternator Pulley. Replace the Serpentine Belt if you see signs of excessive wear or misalignment . Re-install the Belt before the Engine Over-heats. There are some Good R&R Threads on all of these components if necessary here at GMTN as well.

This may be a related issue and is an interesting, On Topic Thread concerning any Question about having 'The Correct Length of the Serpentine Belt':

Can a 5 mm shorter serpentine belt cause problems?

When working on my thermostat I noticed that the belt that's on is a 6PK2320. As far as I know it should be 2325 (mm). Can this cause problems, like engine squealing at high revs, mostly when cold? (I know this can be a pulley but when I had the belt off I tried to spin all the pulleys and none...

gmtnation.com

 

[budwich]

There is a procedure to help "reset" the idle after cleaning. Beside the disconnect / connect time, you also have to let the engine idle for 2 minutes without touching anything. The system then sets up the idle "point" against the known factory settings. If it doesn't help the first time, you repeat the process.

Further, in the video that you posted, your idle throttle position seems low... about half the expected value. Perhaps an indication of "improper idle setup" as mentioned or possibly an issue with throttle body / throttle position sensor / motor.

Lastly, have you changed checked the VVT actuator / solenoid... perhaps it is getting stuck.