Last week I got the AC delco spark plugs that go with my car from the dealership and had a shop change them. I had 143,000 miles on my cobalt so I figured it needed it. Since then I've lost 5 mpg. I usually get 25 mpg going to work 5 days 10 min on the expressway and city driving combined. Now I get 19-20 mpg.Have not tried long drives on the expressway yet. Today I went back to the shop and had them look at the plugs again to see if they had the gap right.They said the gap is correct and they can't tell me why this is happening.
Is anyone having the same problem with their 2008 chevy cobalt 2.2 ?