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you might be running rich.

is there any black soot on the back on your bumper?

 

Thats what i thought and yes pretty much soot above the tailpipe

What could be causing this ?

 

Yep running rich. You may also find that your car stumbles a bit when you first start it in the cold. Do you have an aftermarket fuel pump or regulator? Also, check to see if you're throwing any codes. Running rich can bork your 02 sensors and catalytic converter and exaggerate the problem. Could be a clogged *air filter or an injector problem (stuck open).. variety of reasons that would cause this. It could be blow by (ring seals) or even a distributor problem (igniter coil, pickup cap). Getting codes will help you determine where to start looking first. Do you know how to pull the codes? How do your plugs look?

 

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Okay well the dealer checked the codes with that computer which is how they figured out the 02 was bad. For you to get the codes you need to look under the glove box on the passenger side for a little wire with a plastic clip on the end of it. The plastic clip has 4 inputs on the end. Take a paper clip and jump one of the terminals on the left of the plastic clip to another terminal on the right. Then turn your ignition key forward and it will flash the check engine light in a series of longs and shorts. Each long is counted in tens so six longs would be sixty and each short is a single digit. Three shorts would be three. Six longs and three shorts would be sixty three. FYI 63 is the code for 02 sensor.
Here's a list of all the codes http://www.c-speedracing.com/faq/05.php
PS When there is a broken sensor the computer in the car sometimes adjusts fuel pressure to compensate for what it considers a malfunction which can sometimes cause a rich condition. The faulty 02 may or may not be the original cause of the rich condition. A rich condition can foul an 02 very rapidly. Did anyone at the dealership suggest that you may have bad ring seals? It sounds worse than it is and shouldn't be overly expensive to fix. That's pretty common in our cars and would cause the symptoms you're experiencing. I have a hunch but without knowing more or seeing the car and doing some tests myself, I can't really know for sure.