MPG concerns

[zilla68]

The wife has a 2003 tahoe 4.8l we had bought brand new. It has 98k on the odometer. I drove it yesterday for the first time in a week to fill it up with gas. i figured the mpg at 11.5 so something is terribly wrong, we got a steady 15-18 forever and 20 on the highway.
I asked her why she hasnt been checking the mileage and she said what does it matter. I told her it matters that if it drops a ton we might have some problems.

Only thing ever done to it was 2 batteries and an a/c overhaul under warranty, oh yeah and 2 rear axle bearings and seals (replaced by me). Oil changed with mobil1 synthetic every 3k religiously by me.

I noticed it has a very slight drop in rpms at idle almost like it wants to die, but doesn't and i didn't see a change on the rpms but its something you can feel.

I know its time for plugs, but if the o2 sensor was failing wouldnt I get a CEL

anything else that could cause the drop in mpg other than a math error, but wouldn't throw a code.

thanks ahead of time.

 

[zilla68]

bump

 

[Jarheadgixxer]

Are you wanting to know causes for low rpm at idle or bad mpg? whats your current mpg cause I think anything over 10mpg is good lol.

 

[TunasTwins]

Fuel filter? O2's need to be changed, period. Also look into "seafoam" its a cleaner for the top end, bottom end (engine) and fuel system. dont forget the basics like excess weight in the vehicle and tire pressure. Good luck!

 

[adzam]

I wish I got gas mileage that high!!

Anyway, not sure if it has anything to do with your MPG, but try cleaning the throttle body and changing the fuel filter. That should help with your idle issue.

 

[bottomline2000]

if its anything like my wife's car she lets it sit and Idle forever. Her car was getting 11-12mpg because if it. They don't care and it shows up in mpg sitting reading books and stuff. After I said something about it her mpg went up all of sudden. EZ fix!

 

[Eagle]

Your wife drives like a bat out of hell, and/or sits around idling while waiting for the kids with the A/C on?
that'll drop it from 15 to 11 in town real quick.

 

[zilla68]

a/c has been working overtime due to the 100 plus temps and 50 plus humidity.
Fuel filter is only about 5k old, air filter is clean, and put new plugs and wires on yesterday. Didn't seem to help much for the drop in idle.


When sitting still, idling, all of a sudden the rpms drop off about 200rpm and come back up, kinda just a slight hesitation. Threw my snap on reader on it and no codes found.

I guess I'll just let her drive it till it throws a code, then worry about it.

Are you all serious about the mpg, I remember the first summer we bought it, drove it to San Antonio for vacation, and that thing got 20mpg, I couldn't believe it. I checked it 3 or so times and it was consistent.

---------- Post added at 09:29 AM ---------- Previous post was at 09:28 AM ----------

Are you wanting to know causes for low rpm at idle or bad mpg? whats your current mpg cause I think anything over 10mpg is good lol.

both, the idle drop is kind of concerning to me, and the bad mileage, currently sitting at about 11.5

---------- Post added at 09:30 AM ---------- Previous post was at 09:29 AM ----------

thanks for all the replys

 

[pats hoe]

As far as the idle ,try cleaning your throttle body .Higher mileage the throttle body gets all gummed up and closes off the minumum air gap around the throttle blades for it to idle.Take off your air iintake tube and open the throttle up and clean it out with throttle body cleaner,not carb. cleaner.Ive also used crc or wd40 on a rag and cleaned it too.

 

[donut slayer]

Hey guys, I'm a noob here but here is my $.02, when my wife drives her 04 yukon with a 5.3 she gets 13mpg. When I drive it, I get 17mpg. That may be your answer.