Odd one: car runs rough, for about 10 seconds
 

Okay, so over the last few days, I have noticed that when my car sits overnight, or all day at work, it runs like it's missing on a cylinder for around 5-10 seconds. it smooths out pretty much immediately and i have no issues once its running. Any ideas?

Our S70 has had similar issues lately. Haven't fixed it yet but it's a little hard to start when cold.

Two main suggestions I've heard was the fuel pressure regulator or the temp sensor. Maybe your fuel pressure is low at start and has to build back up.

If you shut it off right away will it do it again?

If so try unplugging you IACV...
I had a similar issue but it was happening almost every time I started the car. I originally thought it was bad gas, but after draining the tank and finding some water, fresh gas it still did it. pulled the mass air, no change.
Then I pulled the IACV... it has not done it since..

Im waiting for my ARD tune to get here tomorrow, im going to install the new IACV and see if is still not happening.

Any smoke out the tail pipe associated with this? Does it sound like an ignition misfire, or like it's running rich?

Also answer to Matty's question would help...

if it gets shut off for a few minutes, or even an hour or two, it starts up just fine. hard to tell with smoke, as I ALWAYS see smoke now that it's in the low 50s/high 40s when I leave for work or get off work....That being said, there's no more or less smoke that I have noticed than normal, but then again I havent really been looking, either.

Wow; that was fast..

I'm thinking maybe a weeping injector; ck for gas in the oil (smell the dipstick). Could also pull the plugs shortly after it happens; look for one or more that are excessively black to see which cyl it is.

If you're seeing excessive steam out the tail pipe then I'd be wondering about possible head gasket or cracked head (know you don't want to hear that..) but you would notice drop in your coolant level...

coolant level hasnt changed a bit. Went out and started the car in the (heated) garage, and saw no smoke. I think I'm good there. I definitely dont smell any fuel under the hood or on the dipstick either.

I think im gonna hook up a fuel pressure tester tomorrow and see where I'm at. If its the FPR going bad, I know that theres a dodge one you can use thats 4 bar instead of the volvo 3 bar. anyone heard anything about this?

problem found: injector is sticking open. Guess it's time to upgrade to the whites....