Hi all, I’ve got a 2005 v6 250k beast that’s starting to give me some anxiety. I just went to start her tonight and upon firing up it kind of stumbled, rattled, and then caught itself. It’s done this once before. Another clue is that it’s only done this when it has been sitting for a few days. My first thought is a small HG leak that pools up over time. I do top off my coolant over time but ide say in 40k miles maybe I’ve put in 1/2gal of coolant…maybe. I immediately check my OBD data and check the misfire logs, when this happens. Sometimes I’ll log 1 or 2 misses but never enough to flip on the CEL. When it acts up I don’t notice any more misses than usual. It’s been cold here so I see steam from the tailpipe but nothing indicative of a failed HG. I can still do a leak down, exhaust gas chemical test, and of course compression but I’ve held off because it always runs perfect. When it’s had its little problem it only lasts a few seconds and then purrs right along. Not sure what to make of it. Again it’s a late 05 so I assume I skated past the HG issues of 03-05.

Thoughts?

You say a late 05...but how late, it's the build date that tells the tale on the earlier HGs, so what is your build date??

12/05 or later will have the new designed HGs, any date before that is the old design.

Pick up a cheap borescope and after a couple days of sitting check those cylinders that get the misfire code. From what I've seen, these seem to dribble coolant into the cylinder when starting to fail.

Curious, what is the first idle RPM when this happens? Could just need a throttle body cleaning as when it's cold it should open up a passage for more air which is why when it's working properly, the idle should start off high.