Tattoodude

Hey everyone I'm new to the forum. So not to sure as to where to post this. Sorry in advance! Long story short me and my wife just bought a 99 Jeep Cherokee Sport with 160,000 miles on it. I've tried to get everything on it up to standard (all basic maintenance). Plugs, wires, cap, rotor button, oil change, air filter, new O2 sensors exc. I'm not very mechanically inclined so most of the time I have to take it to a shop. Yes I know (loser) lol. So here goes. I have a slight rough idle and can't seem to figure it out. I've looked on the forum and checked just about everything I can. Also here's the major stressor I noticed on the forum someone post pics of some sludgy reside/build up on the side of the engine block and they was asking about a blown head gasket! That's my WORRY.!!!! Can anyone tell me signs of a blown head gasket or sure fire way to tell what that might be on the side of the block? Thanks in advance and sorry for the long post.!

thatXJguy

Rough idle and you're worried about a blown head gasket? I wouldn't worry too much about that unless it was a 2000 or 2001.

Explain the rough idle. I would check the idle air control sensor before anything.

Tattoodude

Lol. Yeah I tend to worry alot about everything. I mentioned the head gasket because of what I read the other day about the sludge coming out from the guy's block. Ok rough idle - runs pretty smooth for the most part but when I stop at a red light it has a slight miss/rough idle. I feel it in my foot when applied to the brake and a little in the steering wheel. My wife thinks I'm insane but it's there. Almost feels as if it would need a tune up (if that makes sense). Like the distributor cap is off a smidge! Which I doubt because it was doing the same thing before I tuned it up. It doesn't seem to have a loss in power or anything like that. First thing I thought was maybe bad gas. So changed gas stations and ran some fuel injection cleaner through it and also cleaned the throttle body out. Still has a slight rough idle. Really only feel it when I'm stopped at a red light or in park for a few min. I've thought about trying to clean the IAC! It does sound like I have a vacuum leak coming from somewhere (hissing sound). Sounds like from back of the valve cover. Does that make sense? Or am I just rambling!

cruiser54

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 retracted, the air control passage flows more air which raises the idle speed. When the valve plunger is extended, 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. This should be part of a normal tune-up procedure and whenever idle/stalling issues are present.

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). On 91 and later, it may be easier to just remove the whole throttle body. Be sure to use a new throttle body to manifold gasket when reinstalling.

“Gently” wiggle out the IAC from the throttle body. Gasket/O-ring 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 oxygen sensors. 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 bore itself, the butterfly valve inside of the throttle body and it’s edges, and all associated linkage as long as you have things disassembled

Revised 10-6-2014

Tattoodude

Thanks Cruiser54 , will do! I've been meaning to but the bottom one is a pain to get to. Looks like I'll be pulling off the throttle body, which would be a good time to give everything a thorough cleaning! I'm pretty sure I can do that much without messing anything up. Thanks for the reply!

cruiser54

Removing the throttle body is so much easier like you're saying.

Crazy 8s

It would be just fine to remove the TB to clean it and get at the IAC, but it isn't necessary. It is a bit more work than one might expect, and you will likely need to go buy a bigger Torx bit than you might already have. You will need a new gasket too.

IIRC the Torx bit is like a t60 or t65...

Hope this helps!

Dumajones

Small bit of advice, the screws for the TB body sensors I think are held tight with some lock-tight or something, mine did.
Try to take care and not to strip out the screws head. They will break free but a little tight.

cruiser54

You're thinking Renix. They're easy. The 4 bolt throttle bodies are a bear to remove the IAC from without removing them.

Crazy 8s

Another +1 for the Renix!

cruiser54

Yup.

Tattoodude

Thanks everyone seriously! Me and my wife had a 93 Cherokee and it was a BEAST. I fell in love with Jeeps. That thing was a tank, took everything I threw at it and then some. It hit 315,000 miles and would've taken more but just wanted something with less miles. So when we got this one I've tried going through everything. Well everything I knew how to do (which isn't much lol). I've read the forums for a while and finally joined today. Really appreciate all the help. My hope is to redo everything on this one and really learn how to work on it myself. I drive my wife crazy with the $$$$ it cost to take it to the shops.

Larry's XJ

Second XJ and just joined a forum?

Just think of all the tools you could have bought with the coin you spent at a shop.

$8.00 gets you a pdf factory service manual, can't beat that. Pacific Coast (or something like that) (sometimers kickin)

cruiser54

Well Larry, I think he's in the right place. We'll make a grease monkey out of him!!

CCKen

Yes, it does make sense. A small vacuum leak can affect the idle.


Suggest you get a 3 foot length of 1/2" ID rubber hose to locate the leak. Place one end of the hose tightly to your ear and move the other end of the hose around the area(s) you think the vacuum leak is coming from. See if you can pin point the area then visually inspect. Don't overlook the fuel injectors where they enter the intake manifold. The O-rings on the end of the injectors may be rotten and allowing air to suck in past them.


A crack in the exhaust manifold can cause rough idle due to a fuel mixture upset. Visually inspect all areas of the exhaust manifold for cracks.