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Discussion Starter · #1 ·
Performed tuneup on my 2000STS (118k miles) no change in MPG reading - average is still around 19 MPG. My mechanic changed spark plugs, air filter, fuel filter. Car tires properly alligned.

Could he have not check for proper spark plug gap?
I can't check this easily as I need to dismantle the cover under which they are located.

Greatly appreciate your insight.
 

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mishutka said:
Performed tuneup on my 2000STS (118k miles) no change in MPG reading - average is still around 19 MPG. My mechanic changed spark plugs, air filter, fuel filter. Car tires properly alligned.

Could he have not check for proper spark plug gap?
I can't check this easily as I need to dismantle the cover under which they are located.

Greatly appreciate your insight.
Have you checked for any codes yet? Maybe you have a marginal O2 sensor that could contribute to this problem or dirty injectors? Consider cleaning the throttle body and disconnecting the battery for at least 60 seconds to reset the IAC learned values and ensure an efficient idle.
 

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Discussion Starter · #7 ·
Thanks for all the input. 19 MPG - I was refering to average highway/city mix.
Your opinions lead me to believe it was a stupid idea to plunk down $250 for the tune up in the first place. Why it is recommended to do it at ~100k miles? Just to keep GM parts business afloat?
 
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