Car jerking when at full stop, rpm jump up and down.
Ok after I sea foamed, tuned up, and changed oil on my car. The car starting to jerk when at full stop and the rpm jump up and down. when driving I can feel it too but not as much. When I put my ear next to the exhaust from the back I can hear like popping sound but very low like "boom" "boom". when sitting in the driver seat I can feel that boom coming out. But again its not like the farts that the civics make its a very low popping sound.
what should I do?
Could it be the seafoam? I injected the seafoam in the engine through the vacuum hose. I also put seafoam in the gas. I also had seafoam in the oil but I changed the oil.
The car is
03 V6 Mustang Convertible. 70,000K Stock.