Firstly check that the tyres don't have uneven wear - the front tyres might be worn more than the inside than the outside or vice versa, if they are rotate with the rear tyres, provided they have even wear. Then check your wheel balance, this has to be done in a garage. Hope fully these steps should fix the problem.
1 or more out of balance tires
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12"
Where is the MAP sensor located on a 2003 Cadillac DevilleRead more: [[Q/Where is the MAP sensor located on a 2003 Cadillac Deville#ixzz2R1XaEPL2|http://wiki.answers.com/Q/Where_is_the_MAP_sensor_located_on_a_2003_Cadillac_Deville#ixzz2R1XaEPL2]]
5w30
8 quarts
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The average price range for a good quality, second-hand 2003 Cadillac Deville is $5500 to $7500. The price range depends on the accessories installed, condition and mileage.