Poor gas milage
 

I have a 1999 S70 AWD. I'm only getting about 13mpg City. Don't really drive highway that much. Filled it up with 92 octane and got a similar result. I usually use 87. What do you think the problem is? Air filter, spark plugs, oxygen sensor ? No lights are on on the dash and it accelerates like a beast when it has to and runs fine. I drive very reasonably and don't brake or accelerate very hard. Have only had the car for about a month or less. I know this is still better than an H2, but this absolutely has to be fixed.

Check that Sticky Thread that talks about what to do when you take ownership to a car. Probably needs a tune up, maybe it has cheap plugs. Other than that, check the brake calipers to make sure they are not locking up on any wheel.

Thanks for your response, but I only see the following stickies in this forum:

I don't see anything about newly purchased cars. It's probably go to go to the shop anyway because that's just awful millage. Where do you find the spark plugs anyway?

how do you check to see if one of your calipers is sticking?

Jack the car up and spin the wheels a sticky rotor will be hard to turn. Also if the pad is doing the sticking you will get a brake smell.

also the wheel will be hot after driving, had that problem with my mercedes 560 sl, rear brakes were not releasing, so drive it and put your hand on each wheel and see if one is hotter than the rest

My front wheels are hard to turn.

That is because you are turning the transmission spider gear. If the front wheels are hotter after a short drive than the rear the brakes are most likely dragging.

If you are at 4000 or more then the following things can effect mileage. Baro sensor, MAF, Front EGO Sensor. Below 4000 the Baro is not used as much.

Besides vacuum leaks. I had a repair shop use their Volvo scanner. My car had horrible mileage and was stumbling BAD. I had to feather the throttle to get it to idle. I saw the Fuel mixture reading 17 to 18 on fuel air. Well that is EGO failure or mis-calibration. When I pulled the original Front EGO I realized that they had never been changed. Every 100,000 they need changed I am at 144950. Rear EGO sensor determines if the engine needs to inject air to burn the excess stuff in the Cat.

I changed the MAF because the Car would die after it got warm and then not start up for up to 5 minute. That went away with the MAF If the MAF reports more air in the engine than the EGO reports fuel the fuel injectors will inject more fuel. So it stumbled and died.