I have 3 cars and I was gassing all three up at the local Citgo station. The check engine light turned on the 95 4.6 LX. I think it was for excessive flow. I used a vacuum hand pump to move around the EGR a bit, reset the error code and it would work for a few months and fail again. One day the Citgo station was shut down because a car crashed into the pumps so I filled up at the local Mobil station. The car ran so much smoother and never has had a check engine light for EGR again since I switched it over to Mobil. Any guesses why this might happen? The other two newer cars I own run fine on the Citgo.