My '99 E430 within the last 5k. miles has lost 6mpg highway driving and down to avg. 19.4 mpg. combined with the AC on or off. Was getting 23 combined.I have tried every thing I know to max the mileage..."egg between the gas pedal" coasting to time the red lights..ect. The car has 30k on NGK #7092 plugs,O2 primary sensors around 70k,fuel filter 30k, Air filter 30k,MAF insert 30k cleaned with MAF sensor spray every oil change (8k) Mobil 1 10/30,Can of BG44K every 10-15k, burn top teer primo gas.I have no codes and I have even removed and cleaned the EGR valve /tube with in the last 20k as preventive maintance. Also have alignment done and Michelin primacy mxv4 running at 32psi. Could it just be the Crappy Ethanol gas the goverment has watered down for the past 3 months? Car now has 159,000k. Sugestions welcome!