I know this is a beaten topic but i have searched quiet a bit and nothing really compares to the issue i have but i could be wrong. I just recently put a stock muffler back on my car after running a magnaflow for awhile. I have a catless midpipe on it and have had it on for almost a year. Well once i put the stock muffler on, my car has a decent amount of smoke when its first started up after sitting for awhile and cooling down. It smokes until it barely starts to warm up on the dummy temp. gauge and then all is well. Atfirst i thought it could just be the muffler having something in/on it but its been a few days now and it hasnt stopped. I just find it odd that it hasnt dont this before. It would smoke a tad bit on a start up but nothing like it does now. It doesnt smell like burning oil nor does it look like it. The smoke is a bit thick though. It also doesnt have a sweet smell to it and my coolant level is fine. The oil level is also fine compared to what it usualy is. Im pretty much stumped at this point and have gone over the usual check list. It really does smell like fuel, which if thats the case i dont think i have too much concern. I just hate looking dumb sitting in traffic leaving work, or waiting for it to warm up just sitting in a parking lot.

 

Mine did this for a while after I switched exhausts and then went away, probably just dust and crap in the Exhaust from sitting. Unless of course the smoke is black or if it is white and smells sweet. But if it goes away after it is heated up then it's probably not an issue.

 

smoke or steam?

 

it could possibly be steam... it seems rather thick to be steam though... and yeah once it heats up just alittle bit, it goes away. I really do hate looking dumb in traffic though. But I checked everything over and i see nothing unusual and the car runs fine. I put my hand behind the tip to see what was coming out and there was no oil or sweet smell on my hand. (I used to race motocross so i know what burning oil would looks like) It just smellt like fuel for the most part

 

where do you live? where was the stock exhaust kept?

 

new exhausts always have a burn in period.

 

I live in Hampton roads, VA and I have no idea where the exhaust was kept. It came off an 07 rx8 and it looks really clean. So I'm pretty sure it wasnt kept outside. And its used. Not a brand new exhaust.

 

I recently bought an 04 with 91000 and mine does the exact same thing.

 

Mines doing the same thing, a rough start up with lots of smoke. It's almost like its flooding, which makes me think that it could be a leaking injector but I could be wrong. The longer I let it sit in between start up the worst it is. Is that the same with you?

 

Check your spark plugs (post pics if you want) and have your coolant systems pressure tested and see if water is leaking inside the housings.
That's pretty much the starting point to diagnose such issues.