SOLVED! Rough idle on cold start-up

ChevyGB

New Member
My 2013 Silverado with the 5.3L V8 developed the same rough idle on start-up so many others have reported. 39,000 miles. No trouble codes and the rough idle only lasted a few seconds. After reading dozens of forums with multiple ideas I went with the cheapest/easiest first. Bought a can of throttle body cleaner and took off the throttle body (TB). It was gummed up pretty good with black, sticky dirt. After cleaning it back to original shiny condition I put it back on and the problem went away completely. And the performance noticeably improved as well.
I noticed some people said not to move the butterfly when cleaning, but on my truck the throttle body butterfly is spring loaded to be in the fully closed position when the truck is off (no power to the TB). I could easily open it for cleaning and it sprang back closed. Maybe other year trucks are different. Took about 45 minutes start to finish.
 

Mooseman

Moderator
Hi and Welcome!

Moving the blade with no power to the TB shouldn't be a problem. Did you disconnect the battery during the cleaning (~30 minutes) to reset the PCM? I know we do this on the 4.2 because it's a built-in compensation for the build up. The V8 TB's aren't subjected to crankcase blowby like the 4.2. What do you think could have gummed up that TB?
 

Mike534x

Well-Known Member
Moving the blade with no power to the TB shouldn't be a problem. Did you disconnect the battery during the cleaning (~30 minutes) to reset the PCM? I know we do this on the 4.2 because it's a built-in compensation for the build up. The V8 TB's aren't subjected to crankcase blowby like the 4.2. What do you think could have gummed up that TB?
Funny enough my throttle body on the Envoy had some build up, and the TB on my Avalanche had a small amount but nothing too substantial. The 5.3s normally don't need to be reset from what I read on the TBSS forum, but there is an off chance it'll set off a high idle code requiring a 45 min re-learn procedure to clear it. (Of course this happened to me the moment I cleaned it.)

I'm curious how his had build up at 39k, seems a bit odd to have it with that kinda mileage.
 
OP
OP
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ChevyGB

New Member
Hi and Welcome!

Moving the blade with no power to the TB shouldn't be a problem. Did you disconnect the battery during the cleaning (~30 minutes) to reset the PCM? I know we do this on the 4.2 because it's a built-in compensation for the build up. The V8 TB's aren't subjected to crankcase blowby like the 4.2. What do you think could have gummed up that TB?
Hi.
I did not disconnect the battery but it doesn't seem to be a problem. I'm not sure why the TB was so dirty, but there is a GM service bulletin about oil deposits on the smaller engines TB. It says that when shutting off the engine in cold temperatures, oil vapors will condense with the water vapor and gum up the TB. Or it could be that since I live in California and the poor truck had to breath in thick smoke from the fires last summer for 3 months straight it got good and dirty. Not good for any vehicle.
 

Sparky

Moderator
I know there are warnings about cleaning the TB on the 5.3L the same as thr 4.2L due to differences in idle learn stuff. I have never touched mine for that reason. Somehow mine is not bad at all for having 203k on it.
 
Hi everyone! I too solved my rough idling upon cold start but much differently than what I’ve read as far as suggestions. I joined this group to post my solution and how I fixed this issue to help the next person troubleshoot. My problem had nothing to do with throttle body, but in fact was my oil pressure sensor switch that had gone bad. Bizzare? Yes. Problem completely went away though.
 

Mooseman

Moderator
Very strange indeed. I can't see the correlation between the two at all.
 

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