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Old 04-11-2008, 04:36 PM   #1
99Subprez
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Default 99 Impreza 2.2 only 20 MPG help

My subaru is not doing very well gas mileage wise. I had it checked by a mechanic and he hooked it up to a computer and thought that the o2 sensors were working ok. He did seem to think that the MAP sensor was malfunctioning but, he told me to unplug the vacuum line and see if my fuel mileage went up at all. It went way down, to 17.3 MPG. Before I just start replacing parts, does anyone have any ideas from past history?

Thanks in advance for the help,

Kevin
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Old 04-11-2008, 04:43 PM   #2
SubyRSdriver
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there are A LOT of factors that determine gas mileage.. you shouldnt ever really start going bananas after a bad tank.. or 2.. plug you vacuum back in and give it a few tanks.. also look at your driving habits..
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Old 04-11-2008, 05:07 PM   #3
99Subprez
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This is after driving it for about a month. I haven't got anything better than 20 MPG. I only went 50 miles with the vacuum line unplugged. I was hoping to get at least 25 MPG. Most of my driving is on the highway. Not much city.
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Old 04-11-2008, 05:23 PM   #4
birukun
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SubyRSdriver makes a good point

No cost items:
Air pressure / rolling tire circumference
Make sure you have matching tires and matching tread. Make sure you have the right amount of air in your tires.
Ripping off the massive wing the previous owner put on (just kidding)
remove spare
remove 30 pound subwoofer box+amp

Items that cost
transmission fluid
oil
differential oil
wheel bearings
spark plugs
airfilter

Do you have an Automatic? How many miles?

<------ I have a similar but heavier car and get about 22 mpg (and my 2.2 uses MAP)

If your MAF sensor is questionable, did you try cleaning it? I know there are specific instructions somewhere, be careful because I think a new one is $$$

Last edited by birukun; 04-11-2008 at 05:24 PM. Reason: added stuff
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Old 04-11-2008, 05:24 PM   #5
Kansei
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well in my case you are very lucky... I get about 4MPG. I need a new motor too.
my advice is not where you drive but how you drive. do you like to stomp on the pedal?
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Old 04-11-2008, 05:44 PM   #6
99Subprez
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Quote:
Originally Posted by birukun View Post
SubyRSdriver makes a good point

No cost items:
Air pressure / rolling tire circumference
Make sure you have matching tires and matching tread. Make sure you have the right amount of air in your tires.
Ripping off the massive wing the previous owner put on (just kidding)
remove spare
remove 30 pound subwoofer box+amp

Items that cost
transmission fluid
oil
differential oil
wheel bearings
spark plugs
airfilter

Do you have an Automatic? How many miles?

<------ I have a similar but heavier car and get about 22 mpg (and my 2.2 uses MAP)

If your MAF sensor is questionable, did you try cleaning it? I know there are specific instructions somewhere, be careful because I think a new one is $$$

The car is a 99 subaru Impreza Wagon. The engine has 51,000 miles on it. All tires are the same and inflated to the appropriate pressure. I drive moderately. Not to fast, the speed limit here on the highway is only 60 MPH. I do not have a subs and amps. It is an auto. The oil was just change about 1200 miles ago. No wing! About 3 months ago I had the water pump, oil pump, timing belt, serpitene belt, and the spark plugs done.
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Old 04-11-2008, 06:38 PM   #7
birukun
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I forgot to ask if you are using the A/C

<---- your profile does not show your location

51k miles is not very many miles! If you decide to sell, call me!
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Old 04-11-2008, 06:51 PM   #8
99Subprez
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Quote:
Originally Posted by birukun View Post
I forgot to ask if you are using the A/C

<---- your profile does not show your location

51k miles is not very many miles! If you decide to sell, call me!
What would you offer? The car looks great. And no, the A/C was not on. I live in Colorado Springs Colorado. So elevation might have an effect.
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Old 04-11-2008, 10:56 PM   #9
birukun
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Its your engine I want. LOL

I won't need an engine for another 70k miles, so I am filing your username for when I will need it.

The reason I asked about the A/C is mine is starting to really pull the engine down - I am sure it is going to fail before the end of summer.....
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Old 04-12-2008, 01:57 PM   #10
99Subprez
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Hmm, the engine is staying with the car. I just want to get better mileage than 20 mpg. I am going to try and replace the 02 sensor before the cat and see if that does anything. Any recommendations for brand, ect. . .
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Old 04-13-2008, 02:24 AM   #11
99Subprez
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Oxygen sensor advice?
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Old 04-13-2008, 10:24 AM   #12
birukun
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I ended up going OEM since I could not find the right generic one. I tried the Bosch one that was called for in the 'database' but it did not work. I had to return it and that was no fun.

Order it online and you can save some $$$.
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Old 04-15-2008, 11:21 PM   #13
99Subprez
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where would you recommend to order online from?
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Old 04-16-2008, 05:07 PM   #14
RickRS
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Lightbulb more on mileage

I have three late 90s Subys. My two manuals, 98RS & 99GT, have the cr transmission, ie. 2700rpm@60mph. Here in Upstate NY, both return 25-26 day to day and 30 hwy. My auto Outback gets 20 dtd and 25-26 hwy even though it's gearing is taller. There is that much difference. All have the same 2.5 dohc motor and the same exhaust system.
Subys are never great on mileage. AWD costs 3-4 mpg in my experience.
Oil does seem important. I'm using Amsoil in the manuals and Mobile 1 in the Outback. The Amsoil seems better and it only needs changing every 6mo- 1yr depending on which you buy.
Several years ago I had the Outback's auto trans flushed and filled with all new Subaru fluid. The car's mileage improved 2 mpg. Maybe this will help.
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Old 04-16-2008, 06:54 PM   #15
yarrgh
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get it from subarugenuineparts.com....or something like that. subiegal is the internet sales manager and has always (twice) been great at getting parts to me quickly.
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Old 04-16-2008, 11:20 PM   #16
99Subprez
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Quote:
Originally Posted by RickRS View Post
I have three late 90s Subys. My two manuals, 98RS & 99GT, have the cr transmission, ie. 2700rpm@60mph. Here in Upstate NY, both return 25-26 day to day and 30 hwy. My auto Outback gets 20 dtd and 25-26 hwy even though it's gearing is taller. There is that much difference. All have the same 2.5 dohc motor and the same exhaust system.
Subys are never great on mileage. AWD costs 3-4 mpg in my experience.
Oil does seem important. I'm using Amsoil in the manuals and Mobile 1 in the Outback. The Amsoil seems better and it only needs changing every 6mo- 1yr depending on which you buy.
Several years ago I had the Outback's auto trans flushed and filled with all new Subaru fluid. The car's mileage improved 2 mpg. Maybe this will help.
Thanks for the reply.

Its making me think about switching to synthetic oil for my engine. How many miles are on your auto subaru?
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Old 04-17-2008, 02:09 AM   #17
Tim Sanderson
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Check to make sure your brakes are'nt grabbing. lube the caliper sliders.
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Old 04-17-2008, 03:01 AM   #18
Ioku
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This has a lot to just do with how you drive I have a 1.8 auto and am getting the same mileage, I thought there was some thing wrong so, I did new air filter and fuel filter, new plugs, changed diff fluid, trans, oil, over inflated tires to 42psi, and its still the same, but I don't take it easy on it I push it hard and sort of have to just to get the thing to move, I think I would get better mileage with a 2.5 just because I wouldn't have to push it so hard.
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Old 04-17-2008, 08:00 AM   #19
Hendathor
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Quote:
Originally Posted by Ioku View Post
This has a lot to just do with how you drive...but I don't take it easy on it I push it hard and sort of have to just to get the thing to move, I think I would get better mileage with a 2.5 just because I wouldn't have to push it so hard.
How very true!!! My '97 Impreza wagon gets 25-32mpg consistently, lower of course during the winter months. But I have recorded highway mileages of 34-35 mpg. I drive very conservatively using the "featherfoot" method, I gradually shift through the gears from a stop (much to the consternation of drivers behind me who want you to tromp on the gas!) Keep highway speeds around or under 60mph...it's amazing the gas savings!!!
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Old 04-22-2008, 01:49 PM   #20
99Subprez
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Just to let you all know, I replaced the 02 sensor this morning. The old one was a PITA to remove. I let is soak with PB Blaster for about 30 minutes and off it came! The old one was a BOSH part. Maybe that is why it was not doing a good job. The one I replaced it with is a Denso part made in Japan. I will repost as soon as I fill up again and let you all know if it made in difference in fuel mileage. Again, thanks for all the advice!
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