My 2004 honda civic vp coupe automatic I just got from a reputable subrau dealership is having mpg issues?

I don't gun it or rev it, I'm no ricer. It should get 29 City at least but it seems to get 15. That is not normal what is going on

You will need to see a mechanic with a scanner and check for any codes and get the fuel trims checked. O2 sensors could be failing, the engine has low compression, vacuum leak and/or bad ECT sensor are possible causes. You can get a "tune-up" first and see if it fixes the issue.

Give it a tune & service. (Always do this with a new second hand car that way you know what's due t obe done & when.)

Its probably gonna need a good tune up. New sparkplugs, new air filter, new fuel filter. You can also get some bottle of fuel injector cleaner and put it in to clean the fuel injectors.

Do you have a warranty? Does the warranty cover the engine? If yes to both, then you need to take the vehicle back to that dealer so a mechanic can diagnose the issue(s) and make the needed repairs

now if there's no warranty, then you need to go to a reputable mechanic and have him/her do the same diagnosis… It could be something simple & inexpensive or not

Your Value Package (VP) Civic should certainly come close to getting 30 mpg if it is functioning properly. If you are only getting have that you have one or more major mechanical issues. Time to dump some cash on a good mechanic to figure it out, of live with it. Your choice.

The reputation of the dealer does not matter. Did you have it inspected by an independent mechanic? If not that was a big mistake, always have a used car inspected before purchase.
How many miles on the car?
As for the mpg, start keeping a log. Fill up tank, write down odometer reading, when tank at 1/4, fill up, write down odometer reading and gallons of gas put in tank. Calculate MPG.
As for mpg,
1. Take any extra things out of car. Check spare tire area for water. Proper tire pressure.
2. Get brakes checked. Is anything dragging or hanging up.
3. If past due, get an oil change and new air filter.
4. I'm guessing these are way, way, way past due, change spark plugs (stock recommended is best, ie nothing fancy and expensive) and spark plug wires.
5. Check for vacuum leaks. Change PCV valve.
6. Clean MAF with MAF cleaner.
7. Again probably way past due, change fuel filter, if it is not in the tank.
8. Probably not effecting MPG, but dirty/low/sludgy coolant can cause the car to run a bit hot and cause bad coolant temp. Sensor readings. So if overdue, do a full drain, flush and fill of spec coolant. Not just a drain and fill. See my other posts on this topic.
Those are the most basic things to try first for low MPG.

Your car is 14 years old. Of COURSE, it's NOT going to get the same gas mileage as when it was brand new. Even when new, MOST cars don't actually get the fuel mileage that's listed on their window stickers. The MPG testing for new cars is done INDOORS under computer controlled artificial conditions and DOES NOT reflect real world driving.

Your mileage may vary.

Sensors sensors sensors sensors. Sensors.

Before we pull the cart before the ffuccing horse lets start with just the simple solutions first.

Next time you fill up your gas tanke, let it run to 1/4 full and then add some lucas fuel injector cleaner, and then do the same thing again next time you fill up after that.

That should get mpg back to normal. Then, if you are still noticing some lagging, try some fuel system cleaner. Many would suggest Lucas again but I say maybe go for Chevron Techron or RXP
Then, you should tune up your engine. New spark plugs, spark plug wires, and a distributor cap.

And then if you are still noticing some lag (loss of mpg will usually be accompanied by strange patterns in acceleration) clean (don't replace), clean your mass air flow and throttle position sensors.

Change your oil & test your maf sensor, change or check your spark plugs and make sure they are tightened correctly, get some throttle body cleaner and clean your throttle body and intake manifold with it (you spray it inside the intake I don't mean start cleaning the outside of your engine) and check your other sensors

Car manufacturers lie like wet grass. Mine I have had since new and it never got the acclaimed MPG It gets about 27Hwy. City mileage is worse because you stop and go. And you have an automatic. Change your air filter will help. You might get 19. And the terrain. If you have many hills, and road construction and traffic jams then 15 is where you are stuck at. It is your driving style and terrain and tires and brake adjustment and your body weight that make the difference.

. Did you know that they use the gallon(the imperial gallon(British) which was used in Canada before they went Metric… But is still used in S.A. Because it is Bigger(160oz) than a US gallon?(128oz) 32 oz bigger. When they do the MPG ratings. That is a whole US quart! It is still called a gallon many years before it was called a gallon in the US

. Also their tests are done on a dyno. So in a shop. There's no wind friction to figure with. There's wind resistance if your car is just a square high box on wheels or a super streamlined sports car

. Also reduced is 4 tires or Rolling resistance… Down to 2 tires.

They used to do the MPG ratings by taking the car to Daytona and have it drive the oval track.(more real life highway driving of the car.) as wind resistance and rolling resistance was there.

City driving is at best a guess. Some days you only hit the red lights at EVERY INTERSECTION. Your MPG suffers that day.

Now they are basically fudging the numbers in a non real life setting.

FYI If the car is an Asian brand (and Honda is) it is a Ricer.(aka Asian)vs Yankee vs Pomme vs Krauter vs Wop. Though mechanics find it easier to say the brand name than where it comes from as all car parts are outsourced throughout the world. Asian and English parts are in a FORD or Chev. My Honda came with an Australian made battery. So easier to say Volvo, or Fiat, or Maserati than trying to figure out where it comes from. Nothing is pure anymore.