Gas Mileage worse after Valves adjusted?!
 

I've got a 2006 Acura TSX with 133k miles on it... just had new plugs installed and valves adjusted... gas mileage actually decreased from 30 mpg to 27 MPG on the highway... how can this be? Same commute same gasoline same driving habits... I'm befuddled! Anybody know what might be happening here?

Messed up the valve adjustment?

We'll see... they are an exclusive Honda and Acura repair shop with an impeccable reputation over the last 30 years... I'll be bringing it back there later this week to have them recheck... was wondering if someone knew the technical park behind the adjustment that may cause gas mileage to decrease?

If the valves are poorly adjusted, when the valve stem elongates as it gets hot, it can hold the valve open when the are supposed to be closed; this will definitely impact fuel economy. The other thing to consider is the plugs themselves; it could well be you have the incorrect heat range in there.

The ECU may just be re-learning still.

Is this issue consistent? Or did you note it because it happened once?

Just had the valves adjusted/new plugs put in ~ 1k miles ago...always got 30 mpg before this...

Thanks...that's a big help! It gives me something to ask if they come back and say "everything looks fine"!

Hello Steffin,

I recently had my valves adjusted as well, however it had around 100k miles on the motor. The valves were off, but not by much. I can honestly say however the mpg did increase about .5 which was noticeable mostly on daily drives as the mpg meter showed a higher rate than previous.

The engine also idled much quieter and smoother.

Have you changed anything else other than the valve adjustment?