Rough Idle

I have posted this question before without a response, so hopefully someone else has had this problem.

My jeep idles very rough when the outside temperature gets warm, almost to the point of quitting. When it is cold it doesn't do it at all. When it sputters it seems like the vehicle is not getting enough fuel, could it be a fuel pump?

Any help you fellas could offer would be greatly appreciated. I definitely need to get this taken care of before the temperature gets really hot this summer, and this weekend is a great time to do it.

Thanks

Geoff

Year? Engine? Realavent Modifications?

Sorry, been awhile since I posted, so excuse me being rusty.

1990
4.0
AW4
4x4

Anything else?

Geoff

When is the last time you replaced the following:
Fuel filter?
Spark plugs/wires?
Dist. cap / rotor?
I might be forgetting something but its a start...

Also take your XJ into a garage you trust and have them clean the throttle body. It costs me an hour labor at my local jeep dealer. He removed the throttle body and cleans it then reinstalls with a new gasket. After the tech cleans the throttle body he hooks up the test set and makes sure all the sensors are working right and the idle speed is correct.

My guess is you have a dirty/sticky idle air controller and this will be cleaned as part of the throttle body cleaning.

You could also have vacuum leaks and may want to change out the CCV tubes.

What are the ccv tubes

CCV stands for crankcase ventilation system. It the large and small tube connected to the valve cover. The owner's manual says to replace them every 50,000 miles in my 88 XJ owner's manual.

The front "large" tube connects the vavle cover to the air cleaner. This is the source of air for the interior of the engine. The "small" tube is an orfice and connects the valve cover to the intake manifold. This small tube is how all the gases get sucked out of the crankcase to be burned. The small tube has the same function as a PCV valve but there is no valve on the 4.0 engine.

The large tube comes in two halves, I recommend you get both halves. In addtion to the large tube there is small tubes attched to the large tube my tape which connect to the intake manifold, pressure regulator, air box and EGR solinoid.

Over time these little tubes if you notice an oily film on the connectors for the small tubes indicate they are leaking. I changed mine when i got the XJ in 97 with 102,000 miles and those small tube fittings were loose. I change the large tube assy since the rubber piece in the intake was rock hard and I had to break the rubber it was so hard in order to remove it from the valve cover. The little tubes were just a bonus as paort of that large tube replacement.

I was just trying to think of sources of vacuum leaks. Those CCV harness are often overlooked but are replacement items. When I changed mine I noticed my idle improved.

Thanks for the reminder. I replaced those about 15,000 miles ago.

I will clean the TB myself and see if that improves it at all.

Any other ideas.

Geoff

When you have the throttle body off you need to spray cleaning in the idle air controller (IAC) passage. It the hole next to the throttle body opening. Keep spraying it with cleaning till the cleaner goes from brown to cleaner color. Some people pull out the IAC to make sure the seat it clean and the plunger on the stepper motor is clean.

Also with the idle air controller tube off make sure that passage is clean. One time the mechanic said I had a kitchen match head worth of carbon in that port. If this tube is plugged or unhooked the engine will run horrable. You may want to replace the manifold air pressure (MAP) sensor.