Just posting information regarding my 2005 STS. Found useful information here recently whenI recently started having problems with my vehicle. Approx one year ago i purchased a used engine with approx 5,000 miles, after my original engine blew when my daughter was using it for several months while attending school. Dont really know what happened to it, but it was low on oil when it was brought to my mechanic. When the used engine was installed it didn't run, and only ran when the ignition coil harness and coils from the original engine was used . The engine ran fine for about a year. Several months ago it began running rough and cutting off at stop lights. A diagnostic check showed it was one of the coils. After changing the one coil from the left bank,that the diagnostic machine said it was, the car ran a little better, but still had a miss. Several more coils were changed,but car continued to run rough. The coils that were used were from the original engine. A diagnostic machine then stated that it was one of the injectors. I then went out and bought brand new injectors. Problem was still there. I then checked fuel filter and it was found to be clean. The fuel pump was then checked by my mechanic and found to be working properly.I believe the pressure was 59 PSI. I then bought a brand new maf senor and map sensor and the problem was still there. The last thing i did was to buy all ignition 8 coils with the harness, cost me 159.00 for each side, but the car drives perfect now. I wish i did it from the beginning. The electrical expert that my mechanic used cost me 400.00 dollars and he couldn't find the problem.