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Discussion Starter #1
Recently I noticed a problem when the idle RPM oscillated between 1K and 2K RPM on the 2001 MDX, when the vehicle was stationary. Took it to the shop. They ordered a new Air Intake Valve and just got it back.

The new idle RPM seems to be around 800 now. Also, the MPG on highway has shot up to 30! Earlier, it used to be the usual 20-22 mpg on Bay Area Highways.

While higher MPG sounds great, I am wondering how that could happen. Has the technician messed up some fuel/air mixing ratios? I dont think the trip computer would suddenly go bad.

Any ideas?

Thanks
 

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You most likely had a vacuum leak with the way it was before. Which would cause a lean condition. The O2 sensor sees that and adjusts the fuel trim to richen the mixture to compensate. Which means it's injecting more fuel, thereby increasing the consumption. Now that the leak is all sealed up with the new part, the computer doesn't have to inject so much fuel to keep the A/F ratio right. And that's my best guess as to your mileage change.

Rob
 

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Discussion Starter #3
Rob,

The rated Highway MPG for Acura MDX is 23. After the shop visit it is giving me 30. So it way off the factory desired level, after the part replacement.

My suspicion is more like it is now mixing lesser fuel than before. I am not able to tell but the vehicle may have lost some HP. Also wondering if prolonged operation under the current scenarios will cause any damage.

Anyways, I will contact the Dealer today.

sreeram
 

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Hi Sreeram:

___Did you by chance happen to do a manual check of your fuel consumption? Your next thankful should give you a true idea.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected]
 

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In other words...

The vacuum leak repair may have caused the MPG computed by the trip computer to be too high.

It is also VERY possible that your are only seeing a temporary blib in the trip computer, it may have 'learned' that X set of inputs (including vacuum) translates into Y MPG over the past several tanks. Now that things are different it thinks that X input must mean mean a very high Y, when it resets with the next fill-up, it'l sort things out.

I really doubt that there is anything wrong with the vehicle. There are very, very few things that would result in higher MPG that are harmful to the engine...
 

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Discussion Starter #6
renov8r,

You seem to be right about the "learning" theory.

It does seem to make somewhat over-optimistic predictions (+30%) of MPG at first and seems to self correct the prediction as I keep driving several trips. The Average MPG has been tending down slowly. I will monitor for some more time...

Glad it wasnt another trip to the shop.

Thanks

Sreeram
 
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