rough idle, hesitation. Map sensor?
 

Ok so i have been getting to know my cherokee and trying to diagnose my rough idle and i have a few symptoms. I am guessing its the map sensor. the first time i start it for the day it fires right up and runs great for all of 4 seconds then the idle gets rough and there is hesitation when i step on the gas. then when i start it up again later it cranks a while before struggling to get started. Is this typical MAP sensor or are there other sensors that could be bad here?

Mine done this and it was the map .

Check the IAC.

About to say this .

i had a feeling they might be going bad. ill check them

I have the same problem...but what's an IAC?

Idle Air Control valve. It's plugged into the throttle body next to the throttle position sensor.

Idle Air Control motor or valve. technically its a motor that opens and closes a valve but its semantics. its a motor on the side of your Throttle Body to allow the right amount of air into the engine to keep it idling at the right speed

I've ben meaning to clean mine as well, haven't done one before. I've seen you can use a Q-tip, and that you should be careful not to damage it's "pintle". Guess some day I'll pick up some TB cleaner and take a look at what a pintle looks like!

My can of tb cleaner said I couldn't use it on the iac, that I had to use special cleaner on it (which I didn't) :p

Our Jeeps don't have special coatings on the throttle body or IAC. Just use what you've got.

From 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 Pete, (and Tom). Saving...somewhere in my mess....


Oops, already had it.

Only takes a little longer than checking a CPS. Someone on here was bragging about how easy and quick THAT was...........

I guess by extrapolation I said it takes me three minutes to tie my shoes...:stuart:

He has a 96!^^, (easy Renix CPS test won't work)

Congratulations Cruiser! "Regional Moderator". :clap::clap::headbang::thumbup: