2K1XJ

Went to start the Jeep yesterday and experienced a muffled pop which produced a small amount of smoke from the back driver's side of the engine compartment. Stopped everything and checked for fire...luckily it wasn't ablaze...then it struggled to start...once it did, idles in park at about 1300 and in drive at about 1000 rpm. It seems to start ok now...a little harder than before...but idle is fast.

2001 XJ Sport, 175K miles, probably due for tune up. Still showing good oil pressure and no apparent change in throttle response. Any ideas on what happened would be appreciated.

5150mechanic

Maybe a bad iac or tps?

tjwalker

A tuneup for an 01 consists of a set of freshly gapped spark plugs and check/replace your air filter. Fresh plugs never a bad idea, but probably not related to what you experienced.
But do it anyways.

For a fast idle, I always suspect a vacuum leak and after that, a bad or dirty idle air control. Cleaning can help a dirty IAC.

2K1XJ

Checked under the hood this morning and found a large vacuum hose disconnected at the throttle body. Reconnected it and idle immediately went back to normal. I tried to re-start to see if start up was better and now I have NO start...just cranks and acts like it wants to start.

Now I'm wondering what caused the intake backfire...which probably blew off the vacuum line (it was pretty loose).

XJ Stryker

Does it crank if you unhook it again.

2K1XJ

OK..tried it again with hose connected...NO start. Tried it without hose connected and it started immediately...Thanks Mr. Stryker.

I'm feeling a little dumb now...what do you suppose that means?

XJ Stryker

Take a pic if you could of what you are dealing with. Maybe I can better understand what you are doing.

2K1XJ

Here's a pic...

XJ Stryker

Damn... I dunno since mine is a 87 it is routed differently.

Is that the one that is supposed to go to the Air box. I forget how much different a 01 Valve cover and hoses are to a 87.

I am sure there is someone on here that will be able to shed some light on the subject. If not post up in OEM Tech on www.NAXJA.org

2K1XJ

It goes from the valve cover to the intake manifold (next to the throttle body). It beats me why it wont start with it hooked up...by the way...it isn't throwing any codes yet...but I'll post them if it does.

Thanks

5150mechanic

The iac prob. closed since it was getting air from the vac. leak, you could pull the iac, clean it, with a little pressure push the valve portion back into the sensor then reinstall iac, then start. The idle will prob. go high then lower itself.

2K1XJ

Took the IAC off and cleaned it today (it was moderately dirty). During the process, I somehow managed to break the PCV elbo thing. After searching the valley for a new one, I finally found it and got that replaced. Tried to start the Jeep (with everything connected) and NO GO. So, I once again pulled the vacuum line (from the intake manifold near the throttle body) and it started. The idle was very unstable at first and eventually settled down to about 1100 RPM. My best guess is that the IAC is bad...I'll pick one up tomorrow and see if that does the trick. Aside from high idle, it runs and shifts fine. Any other ideas would be appreciated.

5150mechanic

Cool, let us know how it goes.

Ender

How does one go about cleaning an iac? just curious, sounds like a good idea....

tjwalker

Here you go.....

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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