2003 Deville DHS
 

I have a 03 Deville with 200k miles. For the past year, I've been dealing with a lot of carbon at the exhaust pipes. I've cleanded the top part of the engine twice with Seafoam. I want to know if a defective air pump could contribute to this? I have a MIL code for the air pump. Checked fuses and replace relay and connector along with the solenoid.

I have a burning smell coming from the exhaust and sometimes a grayish smoke will come out after doing a lot of stop and go driving. No problem when doing highway. I also get some valve rattling when moving at low speeds.