Rough Idle When Cold?

[Brewtal66]

Hey Everyone,

Having a weird issue with my wife's 2001 Yukon XL that has the 5.3L in it. Just this week, when I start it up after sitting in the cold all night, it runs on 7 cylinders. Once it warms up a tiny bit, it runs absolutely perfect. No check engine lights or anything out of the ordinary.

The plugs and wires are new, maybe 10-20K on them and they are AC Delco iridium tip ones.

Any ideas where to point me? I was originally thinking maybe bad O2 sensors, but when it's that cold it's running open loop, so that wouldn't make sense.

Thanks for the help/input.

-Tim