I could see how the intake and chip makes mpg worse. If that is the case, then so be it. The intake is so much fun and brings a smile to my face every time I press the gas.

But I believe I probably have this poor mpg due to city driving; my average speed on my car is 17.9 miles per hour. My job is about 7 or 8 miles from my home. My average commute time during rush hour is between 40 and 50 minutes, all of which mostly waiting at stop lights. Now that's city driving at its finest lol

 

Well now, it looks like you just answered your own question.

I just picked up a new to me 2006 SC with 40K on the clock. Drove it back home 130 miles from St. Louis with the first 15 or so miles in stop and go traffic and the remaining on secondary highways with the cruise on 60 mph when I wasn't going through small towns. My trip computer showed an average of 29.4 mpg. Either the trip computer is wildly optimistic or I've bought me a freak of nature.

StillLine

 

Anyone thought or tried CNG Conversion?

 

I think you'll find when you calculate MPG with a pencil and compare it to the trip computer that the computer is optimistic by about 5%.

I have 2 SC430s. One has averaged 20.8 and the other 21.2 mpg. This is actual mpg, not what the trip computer displayed. http://www.fuelly.com/driver/flyct/

I average 21-22 mpg with 30% city 70% highway. http://www.fuelly.com/driver/flyct/sc430

The worst I've done is about 17 and best is 24 average. On the highway the trip computer displays about 28-29 mpg at 72 MPH, depending in headwinds or tailwinds.

JR

 

Turns out the trip computer was a bit pessimistic. Drove the car another 30 or so miles around town and through Giant City State Park. The trip computer had dropped down to 27.4 mpg avg when I filled up to the brim with petrol by stuffing 5.5 gallons in the tank having covered 161 miles. That's 29.27 mpg.

I realized this is just a snapshot with very little data, but I hope the trend continues.

 

I just made a 500+ mile run from Iowa City to Milwaukee, so mostly interstate mpg at 70 mph, rolling hills, 70 degree F weather. Highway mpg came in around 28 using 89 octane, 10% ethanol. My work commute (50% highway at 55 mph, 50% city) has been steady at 22 mpg - but very little stop-and-go and no grid-lock. 177 kmiles on the clock. synthetic oil, ready for new plugs.

 

Hello Gents:
Re Low achievable MPG.

I have gone up approx 15% in fuel efficiency with a detailed clean of my MAF. The temperature sender part of it was covered on one side (the windward side) with tiny particles of dust that wouldn't blast off with the carb cleaner I used, so I soaked it again and gave it a rub with a gentle toothbrush., and it withstood this treatment. I cleaned the throttle body too at this time, as there was some slight amount of gunk on it, though nothing serious.

Then let the MAF dry on a sunny window ledge and plugged it back into the next morning, after doing an ECU reset all night too, and she started first time and runs better than she ever has for me.

The slight stutters and hesitations that were there that I drove through irregardless (as I thought they were a characteristic of that engine and gearbox combination), are all gone now. Amazingly smooth and responsive too. I'mgetting the same acceleration with much less throttle it seems.

 

Cleaning the throttle body will help your MPG.

I need to clean mine and the MAF. I tried to take it out myself with no reference to a manual, couldn't do it.

Does anyone have a link, manual, video, pictures, etc? Anything that'll help.

 

I had the dealer do an injection service flush. They clean the Throttle Body, MAF sensor and flush out the injectors with a chemical. The cost was about $150.

Jr

 

The MAF is at the end of the hose going from your air filter box. Remove the air intake tube, disconnect the cables and tubes and remove the MAF. Cleanit with MAF cleaner NOT throttle body cleaner.

The throttle body is held onto the intake manifold by two bolts that scew in on the right and one bolt coming out held on by a nut on the left. You might have missed removing this nut. Remove connectors and tubes and the TB comes right off. I replaced the gasket with a new one. The inside of the TB was pretty dirty as well as the inside edges of the flapper.

I have never cleaned the injectors - $150 seems like a good price for everything ...

 

Thanks ill give it a try and post an update on the MPG difference.

And I've read some people cleaned the throttle body with warm water, soup and a brush. Is this a bad idea?

 

NO NO NO !!! Unless it's Campbell soup ?

Only joking I knew you meant soap.

Alex, just use a good carb or ideally the specific MAF cleaner fluid in a spray can that is available in parts shops or on line. You'll destroy the MAF's ability to function as designed, with an incorrect cleaning and induce a serious problem with the proper running of the car's engine.

 

There are MAF cleaning instructions on this thread.
https://www.clublexus.com/forums/sc-...-gag-help.html

 

...I think that is manageable,when I hit the highway & set my cruise around 65mph, I usually get 27-28 mpg. But after awhile, thats just to slow for me

 

FYI I just got back from a trip to Savannah GA from Roanoke VA. I decided to check the mileage just for fun. I have an 06 and it is stock. It is interstate from door to door. I drove about 70-75 most of the way. The computer calculated the mileage at 27.8. The gallons into miles was 27.2, This was over about 850 miles so it should be a good comparison. So, the computer is not that far off.