freegdr

Short city driving trips will get you bad gas mileage sensors never reaching proper temps ecm running rich most of driving time.

sycoglitch

This is so true. My city mileage sucks. It's those three short trips to different stores within a few miles that kill gas.

sycoglitch

I totally didn't see you post this before. Yea, these short trips do kill the tank. Or the stopping and going. If weather isn't too bad a factor you can always run slighty higher psi in the tires too.

freegdr

First thing id do is key on key off method of checking codes even if no check engine lights on there could be soft codes also running higher octane fuel will result in slightly better mileage .

Eagle564

Ya i really dont ever have to drive far. Really like 3 miles to work and home, 10 minute trip lol. Unfortunately i know that lowers my mileage but i couldnt imagine by that substantial of an amount. Its probably a large combination of issues. Ill inflat my tires to a higher psi also.

Alrighty ill have oreillys check for codes too

salad

At 11 MPG on a stock XJ almost everything is on the tune-up list. Wires, dist cap , rotor, plugs, oil, filter, air filter, ALL fluids, CCV system, clean throttle body, clean IAC, clean & test TPS, new O2s (OBD-II Jeeps use both), clean MAP, test ECT, test IAT, grease whole drive train, motor & transmission mounts, U joints, tire PSI, transmission throttle valve cable, check for vacuum leaks, clean fuel system, clogged cat, exhaust leak/cracked manifold... You get the idea. There are many threads on this topic

Eagle564

I know theres alot of threads on it but most of em begin and end with someone saying "use teh seerrch functionzz" and thats as far as it gets.

Oil change, dist cap, rotor, plugs and wires, air filter all done recently. Front suspension was greased as well. My tranny fluid looked good when i checked it.

Now ill be honest, i dont know what half of those things are that you listed, nor how id even check them. Ill start with checking the O2 sensors. Fuel system would seem most important from my assumptions but not sure what to do with it. I know i can find a thread on cleaning the throttle body. Not sure what to look for in the exhaust. Ive ran through it looking and never saw any cracks or anything bad looking. All the sensors i have not the slightest clue.

Lowrange2

Search!

Eagle564

Noooooooo! Soo much work involved lol. Well i guess i have to postpone installing my lift yet again. Ill try and figure this out. Thanks for the help guys.

cruiser54

Courtesy of TJWalker:

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The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

"Gently" wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

cruiser54

Also make sure your intake manifold bolts are snug.

Xj88

What is the name of the hose that runs from the top of the head to the side of the air box?

Lowrange2

The CCV hoses?

Xj88

I guess. It just goes directly down to the head.

I broke it

Lowrange2

I picture is worth 13 words.