88cherokeepyles

I'm just wondering if this could be a symptom of something going wrong.

I get 23-24 mpg on the highway when I do a road trip with at least 600 lbs of people and gear in the rig (I'll admit I'm light on the pedal... but not granny style), and in town I get about 10-12. The road trips generally tend to be in high altitude and I live at sea level.

This pattern has been going on for a few months. Its my daily driver but I don't tend to drive it very much in the city, so this isn't a big deal, just a mystery.

A few comments - she surges when idling but never stalls, seems to have lots of power, I've got stock gearing and tires and it's an auto trans 4.0. Also she ticks (speeds up as I speed up) when I rev it up higher than 2,000.

desertempire

It's an 88? If so maybe its your TPS out of adjustment. I might be wrong on this but I think you should be getting worse mpg at high altitude. I had to pull in manual choke on my carbureted vehicle at 7'000 ft because the air was thinner. The ticking is probably an exhaust leak unless you're low on oil. mine ticks above 2300 from the back of the manifold gasket. have you replaced any parts on the engine?

cruiser54

For the idle surging, click on the "pink link" in my signature and do the free things outlined in posts # 1, 2,3,and 6 to begin with.

Make sure your intake manifold bolts aren't loosened up.

Also do this:

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

Neener

If you are at very high altitudes (6k ft plus) you have a significant decrease in air resistance at interstate speeds. Granted high altitude = less engine efficiency but the ECU will correct for lower air density by lowering the fuel output. So even though it takes more throttle at altitude...the fuel consumption may be the same at sea level.
The end is that the difference in the air density at interstate speeds might provide a significant reduction in power needs for any given high speed. Also coasting is AWESOME for fuel consumption.
I can get 28.5 mpg on my one way commute in Colorado (7k to 6K drop over 20 miles)

mister k

Here in CO at 9500 ft I average 20 mpg with my 89 cherokee with 250k miles on original engine.

94JeepCherokeeMan

I get 24.5 mpg on the original O2 sensor... LOL