Im driving a 2001 XJ with a 4.0 engine. It has about 260,000 miles on it and has seen its fair share of issues through the years. Lately, it has been stalling at redlights or generally idling super low (and rough as a result). I notice a small amount of battery drain when this happens, but it always fires back up. The past couple days Ive had to put it in park at lights and rev the engine a little to keep it from stalling out. It also seems to drive fine when the engine is a little colder, and I start having problems once its warmed up.

I had this same problem last winter but thought it had just righted itself and I forgot about it (if it aint broke dont fix it!).

Unrelated to these issues, I just put a new battery in it a couple weeks ago and at the end of last winter I replaced the alternator and a.belt. Im wondering if the alternator belt needs adjusting for the winter?

The check engine light is on and has been on for a while. I tried getting the odometer to read out the codes (hold the trip-reset while turning the key). It cycles through its 1-9 system checks and then just shows the miles on the engine as normal without giving me codes.

I know I can take it to autozone to get the code, but Id rather not drive it down there (the closest AZ to me is kind of far) before asking here.

Thanks!

Idle speed problems can be a lot of things, but I'd start by cleaning and inspecting the IAC, and perhaps putting a test meter on the TPS.
You really need to get the code(s) red, pretty likely they'll point you to the problem.

The serpentine belt doesn't need seasonal adjustments. It does need to be quite tight.

X2 ^

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

Thanks! I bought some throttle cleaner and cleaned the IAC with no luck (tho it clearly needed it anyway). I'm going to get those code read.

Absolutely the next step. You'll need either a code reader or a scan tool. Most shops should read the code for you inexpensively if it's a long drive to Autozone.

The odometer trick will NOT work on your 2001. That luxury went away sometime mid-1997. What you saw is simply a "self-test" of the electronics.

Report back with the EXACT codes (not just a description). With OBD, the devil is in the details.