The most common cause of poor mileage on these cars after worn plugs and bad wires are the engine coolant temperature sensor (the 2 wire one that talks to the ecu) and the knock sensor. The temperature sensor throws no code when it's going south, it simply tells the ecu the engine is cold. When the engine is cold it dumps more fuel to "warm" it up, which never happens so it keeps throwing more fuel than is needed at the motor. The knock sensor cam also fail without a code (they do sometimes throw codes but not always) when it starts to fail the ecu will pull timing and throw in more fuel to combat the knock.

Thanks for the thoughts.  I didn't include this, but I also replaced both engine temp sensors a few months ago as well (no change in mpg with those replaced).  I used sensors from Advance Auto and there was only one choice.  Any issue with those or does it need to be OEM?

 

I haven't done anything with the knock sensor so I'll look to that next. 

I know I see people talk about getting these on ebay.  Anyone have a recommendation for a seller on there?

Edited May 11, 201510 yr by upnorthguy

Seasonally, mpg improves, like now.  But still thinking I may not be getting optimal mpg with the knock sensor code, etc..