rough idle wont run to drive

[Tool24]

Hi new to the site, read a forum where wrencher answered a question and I was impressed. I an a highly trained technician but not on automobiles, I do enjoy the hobbie of trying to fix my own junk. Here is my issue I purchased a Tahoe with a known problem, I was told it needed a new engine, I have owned several 5.3 engines in trucks and found it hard to believe that this engine was bad. These engines seem to be bullet proof to me. I can start the engine and it almost like it has such bad misfires it wont run, the idle is so rough it shakes impossible to drive even though I drove it on the trailer to haul it home. list of what I have done. Cleaned fuel injectors appear to be fine, checked fuel pressure its great, checked all coils and wires and plugs all is well. One thing I found was someone had replaced the passenger side catalytic converter. I wanted to check to see if possible I had an exhaust issue so when I went under I was surprised to find Im guessing when the new converter was installed the cross member bolts were removed and when they were replaced the 2nd O/2 Sensor on the drivers side wires had been caught between the nut and frame and all 4 wire were grounded to the frame. I thought I had found the problem or at least in the right location after undoing and fixing the wires back ( havent put the sensor on yet I need to get one) so I just fixed the wire back just to try and it still has the same problem. one question is maybe due to the short could it have ruined the PCM??

 

Any ideas please help.

[txab]

Done a compression test or pulled the valve covers to see if broken valve spring etc

[Tool24]

I have not, I was looking for what to do next, and when I saw those wires shorted thats what lead me to possibly electrical. If your recommending a compression tesat ill give that a try and see what I find.

[Joel Feeger]

BLEW A fan belt, removed plastic air attenuator, that goes from throttle body, to mass air sensor at air cleaner box.....some how turned mass airflow sensor around.....backwards, truck would start and run rough, when put in gear stall out in 10feet.....DID THIS IN RAINSTORM,,,gave up. waited for the rain to quit, revisited my work,to find MAF sensor backwards....turned it around, and drove home soaking wet Always keep spare drive belt and breaker bar to pull idle pully over allowing belt install

 

OLD TRICK to see what cyls are firing is to use infrared heat gun on spark plugs or exhaust manifold cyls not running much colder sears sell the heat temperature guns for about 30$

[ChevyOwner4054]

Your Idle Air Control sensor may be going out. My truck was idling rough and that fixed my problem. When the truck is idling, you could take out the electrical part for the sensors on your throttle body and if no change occurs, you will have found your problem or at least part of it.

[davekro]

Did you find the problem? Please let us know. Only thing I could think to add is have you pulled the error codes? I invested about $75 years ago for an OBD code reader and it has been a great help for sensor errors pointing to problems that sometimes the Check engine light was not activated on.

[Doug M]

I have a 03 GMC Sierra with the 5.3 idle on it was really rough in cold weather after it heated no more problems. Eventually it got to where it was hard to crank. Turned out to be the upper air intake gasket. The ones from factory are rubber, I bought one from NAPA that was metal and was made better. That fixed all of my issues.