Just recently my car has begun to stumble after it is started in the morning. When I start it, it stumbles and then goes to a normal idle. If I give it a short rev it hesitates a little. It also smells a bit fumey out the tail pipe. I've replaced the plugs, the wires are about a year old, replaced the fuel filter and the O2 sensor (Delco) is about a year old. I've cleaned the TB and the IAC. Didn't mess with the MAF for fear of breaking the wire. I've also checked the coil packs and they appear to be in range of what Techinfo shows. It has thrown no codes.
Once the car gets to operating temp it seems to run fine. Although I do notice a slight rough idle every once in a while.
Any help would be great.