I have a 1988 cherokee with a 4.0. I've been trying to locate a vacuum leak. I have replaced the power brake booster and sprayed around the different vacuum spots on the motor. I still hear a leak around the drivers side of the motor. The idle goes up around 1500 rpm after the motor warms up. When the motor is cold, it idles at 800 to 1000 rpm. Is it possible that the intake bolts are loose?? The cruise doesn't engage and the front diff doesn't stay engaged at speed.

 

Check the vacuum line that goes to the CCV (rear elbow on valve cover)
The rubber is known to deteriorate and crack.

Also, check the line that runs to the vacuum canister (inside bumper-pass. side). The line is a hard plastic and it also cracks. It runs from the intake to the firewall then over to pass. side up then up along the side of engine compartment (alongside the battery and down to the canister.
Often it cracks going thru the radiator support.

Hope this helps

 

I agree with howler, but I will add this you say the idle goes up once the engine is warm, have you sprayed where the intake manifold meets the head, it sounds like there may be a loose bolt, and its spreading with the heat of the engine. Just my $.02

 

Find the leak the easy way.
Engine off
connect a long hose to a intake manifold port.
Blow cigarette smoke through the hose.
Fix where it comes out!

You may have to stuff a rag in the throttle body to keep it in.

 

Intake bolts are easy enough to check. They're right there where the intake meets the head. If you decide to snug them up, work from the middle out to the ends.

 

I'm going to check the bolts on the intake tonight and also replace the o-rings on the injectors. I've sprayed all the connections including the connection between the intake and head.

 

no cruise or 4x4 check line to and from vacuium storage canister behind passenger side of front bumper ,common break place next to battery. as for the idle sounds like time to clean the iac motor

 

Spraying seldom works.
What you spray has to be very BURNABLE. Most carb cleaners, WD-40, water, and the like don't burn.

Since it's closed loop the RPM gets compensated almost instantly. A slight change in RPM is hard to detect.

A liquid tends to wash dirt in the hole, temporarily plugging it.

A good BURNABLE liquid forms puddles - if it ignites a vacuum leak is now a minor issue.

Propane works better, but you cannot see where it's going.

Smoke injected onto the intake manifold won't start a fire, or plug the hole, and is easy to see where it's coming from when it leaks out.


You can buy a smoke machine to do it - $800 - $2000, or use a cigarette for pennies.

A little logic goes a long way!

 

Easy smoke method

 

The cigar - it worked for Monica Lowinski.

 

On my 88 xj I cannot fimd this black cannister locater behind the bumper on the passenger side, its beencapped off since I bought it, how do I fix my issue ? Lol, also I have a hissing possibke vac leak maybe top of fuel tank its aroumd my tank, filter and other hoses all r good.

 

Sometimes a loud humming fuel pump is mistaken for a vacuum leak sound.

As for the missing cannister, go get one at the JY. Note how the hoses are routed and install it on your Jeep.

 

Hmm fuel pump thst noisy? Well few weeks it gonba b replaced its all original I think at 250000+ miles earns a new one with new filter and already new lines lol

 

Also the canister, how do I kno if its been relocated? Can I just leave it blocked off?

 

They can be slightly noisy where they sound like a hissing sound or they can whine like a cat who's tail got under the rocking chair. And, everywhere in between.