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When I say rough I mean like bad 70s carbureted motor rough. I've never seen an injected motor this rough during warm up. On the coldest days, it can even die out on me. The problem has only popped up since temps have dropped into the low 30s here.

I changed my plugs and wires according to GM spec a few months back so they should be solid. Oil is good ... at least Oil Stop says it is. Everything else seems fine and it runs great once it's warm.

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Checking for DTCs (error codes) may provide some useful information. Temperature sensors may be something to look at as well. – mac Dec 18 '12 at 14:37
Which engine does your vehicle have? – Mark Johnson Dec 18 '12 at 14:53
5.3l, just added to the title. – plainclothes Dec 18 '12 at 17:06
@mac When my idle first started getting choppy on cold days I had all the pertinent sensors checked out. Of course, that was several months ago. – plainclothes Dec 18 '12 at 18:32
up vote 4 down vote accepted

Looks like I may have answered my own question last night. I did a deep clean on the throttle body (and as far back in as I could access). The idle is HUGELY improved, though still not perfect on this 28° morning.

Is that really all it was? I'd love to hear your comments if you've had the same experience.

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Looks like that did it. I've scrubbed throttle bodies many times before, even some really dirty ones, but I've never seen such a dramatic result. I had no idea a little surface grime could destroy cold idle. – plainclothes Dec 19 '12 at 5:33
Depends - if it was grimy enough so it wouldn't close properly, that would mess up the idle something fierce. – Timo Geusch Dec 24 '12 at 22:10
@timogeusch not even close. It was just surface grime. A few swipes with a cleaner doused shop rag did the trick. – plainclothes Dec 24 '12 at 22:36

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