Hi there

I've finally got my dream LS430-2001.
The problem is my average MPG is around 15-16 (city), reaching 20 on highway (Which i will not criticize for now), BUT if I stopped by anywhere leaving the car on neutral. That MPG number is rapidly decreasing ( it can reach down till 8 or something ). and It won't increase again unless I start to drive the car again...is that normal?
I have recently cleaned throttle body, replaced all spark plugs with OEM plugs, checked all coils (one was faulty and got replaced also).

Anything else can be done?

Thanks guys

 

Does this rapid increase happen after the avg mpg has been reset recently? You are getting 0 mpg while you are sitting still, so if you have recently reset the value, it's normal....not sure how to best explain, but say these are like at bats for a baseball player. While you are standing still you are striking out, over and over, lowering your average. Then, the faster you can cruise, the more you are getting hits. Over your career, one more strikeout won't even change the average. But in a single game, a strikeout will lower your average.

 

Yes!, I did reset my avg mpg counter yesterday.. so that's the reason then, many thanks buddy

 

No worries.....the first time I ever saw a mpg computer, was on a Chevy Cruze rental car, and I was observing how it was behaving because it was new to me. The one feature I like about our LS', and I'm not sure how it knows, is that whenever we fill up, it resets the tank avg. So even if we were to reset the computer, the car is storing the tank avg., This would allow us to experiment with resetting the mpgs, without actually losing the overall tank avg. For example, get up to 65 mph, and reset the avg. mpg, now drive as far as you can (30+ miles would be nice). That number should be pretty high, my car would likely be 27-28 mpg for this highway only drive...

I find the Lexus number to be close, based on how many gallons are pumped, the Lexus computer number seems just a little optimistic, not much though....for me, maybe 2 to 3/10 mpg better than reality....my wife's car is way off, her computer shows her using much more fuel than the pump says....(the pump has to be correct)

 

Did you clean the maf? Also probably should disconnect battery to relearn everything after cleaning and replacing parts.

I just took a trip the other day in my 04 ls430 about 130 miles total and averaged 22.4 mpg..... But I was cruising at 100mph most of the trip. Not bad actually and my car is lowered, with 20 inch rims as well.

 

Update.
Thanks guys, I used the "reset" button on the right side of the steering wheel, then made about 50 km trip (cruising on 100-120)... got around 22 mpg and now the MPG is not anymore decreasing on idle!