cdf43

87 cherokee 4.o 5speed

ive used the search feature and found some info, but i couldnt find my exact problem

at idle the rpm will slowly get lower and lower to the point were it almost dies then on its own itll rev its self up to about 1000 then slowly get lower and lower till the engine shakes and wants to die, then on its own will rev back up to 1000.

im going to do some work this weekend on it but im just trying to do some research...theres no obvious vacum leaks, i was thinking the TPS or IAC...someone told me the CPS but if that were messed up wouldnt it not start? im going to clean the TB and the IAC and see if that helps

also my PCV or CCV or whatever you call it....the elbow on the front of the VC is cracked, i dont know if this would have anything to do with it but i thought id mention it

thanks for taking the time to read this and i hope you gys can help

BigBear

That can be a number of things.

1: Vacuum leaks

2: EGR valve.

3: Air filter

4: Fuel pump

5:Leaking head gasket

6:Timing chain worn

7:Camshaft lobes worn

8:Valve clearance out of adjustment

9:Ignition timing out of adjustment

10: Thermostatic air cleaner not working properly

11: Choke not working properly

12: Dirty or clogged injectors

13: Idle speed out of adjustment

Hope this helps.

cdf43

thanks for teh input, what should i start with, i dont want to throw parts at it or chase a wild goose if you know what i mean....i am on a budget

freegdr

most common item is the IAC remove and clean it and the mounting hole in throttle body

Mendax13

well i would say its doubtful that its the cps because you're right it wouldn't start. or it would just quit running not fade and come back like you're describing. Good Luck!

tjwalker

The Idle Air Control (IAC) is mounted on the back of the throttle body. 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

Reinstall IAC and check idle quality

cruiser54

Good advice there^^ and requires no parts, just a can of throttle body cleaner.

cruiser54

Good advice there^^ and requires no parts, just a can of throttle body cleaner.

cdf43

thanks a lot guys, im going to try it out this weekend, ill let you know how it goes

cdf43

so i drove it around the block and it feels like a TPS or choked up TB. randomly it will lose power but if i crack the throttle it will bounce back and take off

cdf43

update

filled the tank with good gas, added fuel system cleaner, checked for vacuum leaks useing carb cleaner. cleaned the throttle body and throttle plate, which wernt to bad. cleaned the IAC.

problem still there.

what steps should i try next

CattyXJ

Get a multimeter and a Haynes manual and start checking sensors if you don't want to throw a lot of money at it...

cdf43

which other sensors besides thr TPS and IAC

CattyXJ

Definitely check the TPS and IAC. Cleaning the IAC doesn't mean it's not faulty. I believe your year had a MAP, or manifold absolute pressure sensor (could be wrong) the coolant temp sensor, etc all have to to with air fuel mix and how your jeep is running. The only way to know for sure is to find and check them. My Haynes manual is my best friend when it comes to my jeep. It gives you almost any piece of info you could need, including the electrical specs on all the sensors. Just my 2 cents

cdf43

alright thanks a lot. i dont have a haynes. but i know i should get one