Intermittent rough idle and performance

[Matahoe]

Hey everyone.

For the most part the 5.3 liter engine runs great. However at times more often than not the engine has a very noticeable rough idle. Not so much rough on a consistent per revolution but rather a definite hard stumble or as of someone injected water into the engine at random and the engine suddenly becomes rough. Seems to be worse with A/C on but there regardless.

Over the past year my 2005 Chevy Tahoe LT has been tuned up with new plugs, wires, coils and fuel pump along with all filters. Even had a complete Trans fluid and filter plus all other driveline fluids changed. I did all the work myself.

About the only thing that may be related... i had the plug wires reattached a few months ago and i cleaned the engine with some degreaser. After rinsing i noticed a large snapping on the rear passenger side. Could this be the source of the roughness i am experiencing? I am a very thorough aircraft mechanic. Fearing an intake leak i had new Felpro intake manifold gaskets and knock sensors installed. Good thing I did that as the knock sensors were heavily corroded. Also changed knock sensor harness as well. Torqued manifold to spec. A job very thoroughly done.

Still even with all that the cause of this roughness is eluding me. Fuel pressure is 49 psi with KOEO and 60 with engine running. Brand new Bosch oem fuel pump by the way. Original pump was badly corroded and leaking. Fuel lines have seen better days. Had to replace some of the fuel line connectors with Dorman nylon connectors. I suppose i did that correctly as i have no fuel smell. But pressure drops off rapidly with KOEO. Do i need a new pump? Thanks for any help!

 

[Rivieraracing]

Even though you talk about your intake gasket work, I assume you cleaned your throttle body while doing all that? If not, I'd look there first!

 

[#1taho]

Look at night and see if you can see sparks from the passenger side. I think you have a bad wire. But I would also check what rivieracing said also. Losing pressure I think is not a good thing. I would investigate that a bit more. I think is may be on the way out.

 

[Matahoe]

Even though you talk about your intake gasket work, I assume you cleaned your throttle body while doing all that? If not, I'd look there first!

Brand new throttle body, intake manifold cleaned inside out. Old GM intake gasket had noticeable missing silicone material missing around many cathedral interfaces. Vehicle has more getup and go after intake manifold and knock sensor replacement. Had an issue with engine pinging at heavy/wot loads but the previous gasket and knock sensors fix solved that. Overall though the rough idle is still there. At times the idle is very smooth but these events are exceedingly rare.

 

[retiredsparky]

At night use a spray bottle with water to spray around the spark plugs/coils, especially on the passenger side where you heard the snapping. You may see some sparking indicating the high voltage wire or bad coil arcing to ground.

 

[Skip Santos]

I purchased a 2003 Tahoe LT with 126M miles on it at the end of July. It ran fine. After a few weeks, it began to miss and had no pick up and would not go over 40 mph. I am not a mechanic so I brought it to a friend's cousin who is the manager of a service department of a large dealership. He found that it was a clogged catalytic converter (no rattle). He replaced it and all is well.

3 of his mechanics all had different opinions as to what the problem was, so he drove it and identified the problem. He told me that I was fortunate that I brought the vehicle to him as he has seen this only a few times in his 35 years of experience - meaning that it was not a common problem. Had this not been identified early on, it would have been quite possible that a variety of work would have been performed without resolution - in other words - it could have cost a good bit of money until the true problem was identified.

All of that said, this may be no where near where your problem is, but I figured this is worth sharing since all other does not seem to be working. Good luck.