05' Z71 Tahoe stupid idle
March 5th, 2017 | 2:49 AM
#1
Thread Starter
CF Beginner
Joined: Mar 2017
Posts: 2
Likes: 0
05' Z71 Tahoe stupid idle
I'm new to forums. This is my first. Have an 05 Z71 Tahoe with 230K. Rough idle, worse as it gets up to temp. Starts fine, runs/idles great thru the open loop. Give about 30-40 seconds and let the misfires roll. If I mash the gas while in park, it responds like a champ, then drops back down to about 550-600 rmps and picks back up with the rough idle. However, if I raise the rpms up to about 650 and let off it nearly dies then goes back into its rough idle.
This machine runs runs great on the road, no lack of power anywhere, no misfires, perfect! Hooked up the Snap On Solus to check. It shows THE DREADED PO300, but only cyl #7 is misfiring. 20 to 40 misfires at a time. When I put it on the road and drive, everything looks great, misfires go away..
When I bought this it did NOT have cats.. I test drove it 3 diffrent times. Noticed the misfire on the second drive. Figured I could fix it relatively easy. I own a 2001 4x4 Suburban LT with 260k, runs like its new., a 2000 Z71 1500 xcab with 200k, runs like a champ and a 2500 4x4 ecab longbed with a 6.0L with 255k, runs like a beast.. This 05 Tahoe runs great just a stupid bad idle!
Here's the scoop on this so far...
Fuel pressue is 53psi steady..
Compresion on all cylinders are 150-155..
New plugs and wires..
Replaced intake man gasket.. (old one was sealing fine, vac is 17psi, drops a bit during misfires)
Switched #7 and #3 coil... (misfires still stay on #7)
Cleaned and checked all injectors.. (node'd out good, made test stand for injectors and misted perfect)
Switched #7 and #4 injectors.. (misfires still stay on #7)
New throttle body.. (got super cheap, did relearn, no change)
Tested ALL O2 sensors... (Replaced both upstream sensors. B1 looked rich, B2 looked good)
All 4 tested out fine..
MAS is good...
MAP is showing kpa 33-40 at idle (changes with misfire, don't know what it should be)
Removed valve covers.. (springs look good, no noticable cracks in the head, turned over engine and rockers keep consistent rise, with precision straight edge across the board. I would need to set up an indicator for true measurments but were talking a few thouands of an inch)
I'm not a pro with the Solus but it has always led me to the sure fix with my fleet of 7.. that is until now.. Could this be a bad injector driver on the pcm? If so, how can I test it? Valve seat to deep was suggested, but if that was the case, the timing would be off enough that the compression in that cyliner would be lower??? I think... I'm at a loss here. Any suggestions would be awesome..
This machine runs runs great on the road, no lack of power anywhere, no misfires, perfect! Hooked up the Snap On Solus to check. It shows THE DREADED PO300, but only cyl #7 is misfiring. 20 to 40 misfires at a time. When I put it on the road and drive, everything looks great, misfires go away..
When I bought this it did NOT have cats.. I test drove it 3 diffrent times. Noticed the misfire on the second drive. Figured I could fix it relatively easy. I own a 2001 4x4 Suburban LT with 260k, runs like its new., a 2000 Z71 1500 xcab with 200k, runs like a champ and a 2500 4x4 ecab longbed with a 6.0L with 255k, runs like a beast.. This 05 Tahoe runs great just a stupid bad idle!
Here's the scoop on this so far...
Fuel pressue is 53psi steady..
Compresion on all cylinders are 150-155..
New plugs and wires..
Replaced intake man gasket.. (old one was sealing fine, vac is 17psi, drops a bit during misfires)
Switched #7 and #3 coil... (misfires still stay on #7)
Cleaned and checked all injectors.. (node'd out good, made test stand for injectors and misted perfect)
Switched #7 and #4 injectors.. (misfires still stay on #7)
New throttle body.. (got super cheap, did relearn, no change)
Tested ALL O2 sensors... (Replaced both upstream sensors. B1 looked rich, B2 looked good)
All 4 tested out fine..
MAS is good...
MAP is showing kpa 33-40 at idle (changes with misfire, don't know what it should be)
Removed valve covers.. (springs look good, no noticable cracks in the head, turned over engine and rockers keep consistent rise, with precision straight edge across the board. I would need to set up an indicator for true measurments but were talking a few thouands of an inch)
I'm not a pro with the Solus but it has always led me to the sure fix with my fleet of 7.. that is until now.. Could this be a bad injector driver on the pcm? If so, how can I test it? Valve seat to deep was suggested, but if that was the case, the timing would be off enough that the compression in that cyliner would be lower??? I think... I'm at a loss here. Any suggestions would be awesome..