Sluggish Cold Starting For ~5-10 Secs. - Runs Fine After That
 

2009 LS1 85k miles, orig. sparkplugs, air filter changed several times

As the title says, it's a little sluggish and "sputtery" starting for about 5-10 seconds when the engine's cold. No stalling and it always starts. After that it runs and drives fine. If I stop at the store a few minutes later, it starts fine.

This started after it sat two-and-a-half weeks when I was away in Jan. and before the trans. started acting up (see my other thread). It did have a code for "rich mixture" (can't remember the number) but no CEL. I cleared it and it didn't return. (After that the trans. had trouble and I forgot about the code.) It sat again for a week-and-a-half in Feb. and hasn't had a lot of use since. I thought the start issue was from sitting and would clear up after some use.

The battery was disconnected/reconnected during the trans. change.

It seems early (85k) to replace the sparkplugs, but I'll check the air filter depending on the weather (no garage) but I'm wondering if anyone has other suggestions. I'll check for codes tomorrow.

Check the throttle body, it probably needs to be cleaned.

Check the EVAP purge valve; disconnect it completely then blow into it; if it is blocked it is good.

Check the fuel pressure, the check valve may have gone bad.

Thanks, guys. There are no codes and none pending. I checked the easiest thing first, the air filter. Lots of acorns (damn tree rats!) sitting on top of the head when I took the filter housing off and debris stuck in the filter which was also due. I guess a squirrel got in there while it was sitting for two weeks. I had MAF sensor cleaner so I cleaned that and put a new filter in. I didn't have any throttle body cleaner to do that. I'll see how it starts tomorrow.

Just wondering, though, if the EVAP purge valve was bad, would it affect idle, acceleration, etc.? All of those things are fine. Idle is very smooth.

Not necessarily, but, it leans on startup right when you want rich.

Which is why you can get a false rich code; the computer is trying to correct for the lean condition that does not really exist. The O2 sensor says "lean" the MAF says "whaaat?" the computer adds fuel. Convoluted!

Thanks. I'll check it when it gets nicer out, raining right now.

No change after new air filter and MAF sensor cleaning. I'll check the EVAP purge valve in a couple days; it's due to warm up for the weekend. I ordered one from Rockauto so I'll have it if I need it.

Update soon.

Batteryyyyy

I think I'll have it checked at Advance Auto Parts; if I think they'll check it for free.

Battery, charging, and starter all check out good; next step is the EVAP purge valve in a couple days.