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Hello!

I recently helped my girlfriend purchase a 2005 Acura MDX with 130K miles on it. The vehicle had been sitting for about a year and a half before it was sold (the owner advised us, plus we could tell because the last oil change was a year and a half ago and they had only put about 200 miles on the vehicle since then. We really like the MDX, with one glaring exception that is a total deal-breaker. It gets absolutely horrific gas mileage around town (as in 9 MPG). Interestingly enough, we took it on a trip to Las Vegas and during the trip, we got 21 MPG. She almost solely drives around the city though and we are getting like 210 miles on a full fill-up before the thing is on empty (I have calculated both manually and with the trip calculator screen and they both yield very similar results). There are no check engine or maintenance lights on the vehicle and it just passed smog last weekend.

I have tried the following steps to see if I could improve the gas mileage, in this order without success:

1. Changed spark plugs
2. Changed air filter
3. Sea foam in gas tank
4. Sea foam in vacuum lines
5. Lucas Oil fuel injector cleaner in gas tank
6. Replaced EGR valve
7. Took to mechanic who hooked it up to a machine and said that all readings that have to do with fuel economy are within normal range.

Last weekend, we took it to the local Acura dealership to discuss if there were any other options and the service manager told us that an SUV of this age with this many miles on it would be expected to get about 9 mpg in the city and that this is NOT unusual at all. I was completely shocked by his statement, but he said that he would guess that's about average based on conversations with folks who bring their older MDX's in for service. He offered to do a valve adjustment for $999.99, which may offer a slight improvement to fuel economy. However, he wouldn't guarantee anything and told us that it was unlikely that the improvement would be very dramatic. He said that it may improve it by one mile or so per gallon if we are lucky.

From combing this forum, it would lead me to believe that 9 mpg is VERY UNUSUAL, even for city driving with a fair amount of stop and go. With that said, we are located in Orange County, CA so I would guess that traffic is worse here than other places. At this point, we are ready to sell the vehicle if we can't get reasonable city mileage out of it (like at least 14 MPG). However, I figured that before we take that drastic step, I would post here to see if anyone else has any ideas for us.

Thanks,

Tim
 

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I would also change the pcv valve mine was totally clogged. I get around 16-17mpg in mixed city/back roads with 200k miles.
 

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Discussion Starter #5

Get a cheap scan tool and check fuel trim levels?
Thanks for the link to that site. It looks like 9 mpg is at the very low end of the bell curve for individual fill ups although 12 mpg is the very low end overall for the vehicles in their system. When you blend in the small amount of highway driving she does, we're averaging about 11.5 mpg.

Unfortunately, the mechanic that we brought it to already checked the fuel trim levels and said everything was within range.
 

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The air filter would be the most likely suspect if it hasn't been changed lately (nothing will improve your mileage as much for so little money as a new air filter). I got a 1mpg bump by tossing the K&N air filter the PO had installed). ;-)

Another thing I did to my MDX (without a lot of improvement though) was to replace the upstream (pre-cat) O2 sensors. Those are the ones that tell the computer how much gas to inject, and they DO wear out over time (anything over 100,000 miles is suspect).

The PCV is a no-brainer. Super cheap, dead easy to swap, and likely to be a problem.

And yes, a valve adjustment WILL improve the way your MDX runs.

The bad news is that it's still a 4,400 pound all wheel drive SUV, and as such is never going to get good gas mileage in the kind of horrific traffic you have in your area. If you're having to mash both pedals continuously to drive the car during "busy periods" (in SoCal, that's pretty much any time) you're never going to get close to "normal mileage" on any vehicle... physics is a cruel mistress. In the end, if you're getting 21mpg on the road, that would tend to indicate that your vehicle is getting about as good a mileage as it's ever going to get (I never did better than that on any of my road trips, though I averaged about 80mph on the highway portions, being in the west).
 

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Discussion Starter #7 (Edited)
air filter the PO had installed). ;-)

Another thing I did to my MDX (without a lot of improvement though) was to replace the upstream (pre-cat) O2 sensors. Those are the ones that tell the computer how much gas to inject, and they DO wear out over time (anything over 100,000 miles is suspect
The bad news is that it's still a 4,400 pound all wheel drive SUV, and as such is never going to get good gas mileage in the kind of horrific traffic you have in your area. If you're having to mash both pedals continuously to drive the car during "busy periods" (in SoCal, that's pretty much any time) you're never going to get close to "normal mileage" on any vehicle... physics is a cruel mistress. In the end, if you're getting 21mpg on the road, that would tend to indicate that your vehicle is getting about as good a mileage as it's ever going to get (I never did better than that on any of my road trips, though I averaged about 80mph on the highway portions, being in the west).

Thanks man. Appreciate your feedback. Yes, recently did the air filter and unfortunately, it didn't make much difference. I'll swap out the PVC since that's easy and cheap. I was thinking about doing the upstream O2 sensors as well and those are pretty cheap so I'll probably just swap those out as well for the hell of it. I'd do the valve adjustment if it wasn't so damn expensive. Maybe I'll check with my regular mechanic and see if that's a service he can do for cheaper than the dealership.

Yeah, I understand that it's a big vehicle and that due to the area we live in the mpg would be worse than expected, but I wasn't expecting it to be this BAD. Oh well. If I get any improvement, I'll post back here. If not, we'll probably end up selling in the next couple months and getting something more economical.

Tim
 

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Highly recommend swapping the o2 sensors out, bank 1 sensor 1 (behind engine closest to firewall below ignition coils), bank 2 sensor 2 (on front of engine below ignition coils) get a 7/8" specialized socket. I just did this job and wow. What a difference.



 

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Highly recommend swapping the o2 sensors out, bank 1 sensor 1 (behind engine closest to firewall below ignition coils), bank 2 sensor 2 (on front of engine below ignition coils) get a 7/8" specialized socket. I just did this job and wow. What a difference.



Great, thanks! Will give that a try next. So when you say "what a difference", do you mean that it drastically improved your MPG?
 

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Great, thanks! Will give that a try next. So when you say "what a difference", do you mean that it drastically improved your MPG?
I actually had one that was intermittently throwing the check engine light on along with the VTM-4 light. I replaced both and noticed about 4 mpg increase as well as night and day difference in shifting. Shifting used to be rough, but now is extremely smooth in comparison.
 

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I actually had one that was intermittently throwing the check engine light on along with the VTM-4 light. I replaced both and noticed about 4 mpg increase as well as night and day difference in shifting. Shifting used to be rough, but now is extremely smooth in comparison.
Great, thanks!
 
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