1997 SE 3.8 with really bad mileage, what can i do?

[x1lightning]

last year i picked up a 1997 grand prix SE with the 3.8
and ever since i got it the mileage has been really bad, on a road trip, the best i can do is 23, usually its like 20, and i drive pretty normal. and i keep my tires at 40 psi

I changed the plugs on the car and the air filter, and that didn't have any effect on it. i noticed that the intake manifold gasket has a light leak and i'm going to replace it, could that be causing the really bad mileage?

if not any other ideas on what could be wrong with it?

thanks

 

[blueguy]

Fuel filter? Try that too...

 

[x1lightning]

i will try that, i didn't realize that a fuel filter can make the mileage go down....

 

[blueguy]

Change the oil and oil filter...clean out the throttle body...you'll see all of the gunk. I'd get new plugs wires and pull of the coil packs and try cleaning those too. And if all else fails throw some Lucas Fuel System cleaner in the gas tank. I used that on my old Buick ('86 Iron Duke 4 banger) and it gave it AT LEAST 3-5mpg better after I ran it though...although they recommended it for F.I. cars I had T.B.I. and it worked just fine

 

[x1lightning]

Change the oil and oil filter...clean out the throttle body...you'll see all of the gunk. I'd get new plugs wires and pull of the coil packs and try cleaning those too. And if all else fails throw some Lucas Fuel System cleaner in the gas tank. I used that on my old Buick ('86 Iron Duke 4 banger) and it gave it AT LEAST 3-5mpg better after I ran it though...although they recommended it for F.I. cars I had T.B.I. and it worked just fine

what should i use to clean out the throttle body?

 

[Pontiacman]

The tires don't need to be at 40psi. They need to be about 30-32 psi.

 

[x1lightning]

i have always done the 40 psi on my cars and usually gained me an extra mpg, but on this thing didn't make a difference, so maybe i should lower it