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Welcome.
It sounds like your cars engine management system is working as designed.
Here's some low hanging fruit. (low investment)
Partial grill block.
Inflate tires 44 to 50psi. Check the sidewall of tire for suggested max.
Install a vacuum gauge and try to maintain highest reading when at cruise. Or better yet, install a MPGuino. Instant feedback is very important in order to refine your skills.
http://ecomodder.com/forum/showthrea...uide-3428.html
MPGuino - EcoModder
OpenGauge / MPGuino FE computer - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
Read about more tips here.
65+ Vehicle modifications for better fuel economy - EcoModder.com
And here.
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com
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