The idle on the 1998 Jeep Cherokee is controlled by an idle air control valve. This part works with the vehicle’s main internal computer to regulate the air and idle speed of the engine. You cannot manually adjust the idle on the Jeep Cherokee, but you can clean the grime buildup on the idle control valve to fix rough, high or unstable idle speeds. If that doesn't work, you can replace the part to regulate the idle speed once again.
Open the hood of your 1998 Jeep Cherokee. Find the throttle body straight back from the A/C compressor, to the left of the fuel injector and to the immediate right of the air intake temperature sensor on the engine block. The idle air control valve is a black plastic part approximately two inches long that is attached to the throttle body.
Grab the oval electrical connector that is connected to the idle air control valve and pull it away from the valve to disconnect it.
Use a Phillips head screwdriver to remove the two screws that hold the valve in place.
Use a rubber mallet to tap the valve body loose from its position.
Thoroughly clean the idle valve with a shop rag and an aerosol carburetor cleaner. There will be a build up of oil and carbon on the valve that may be causing your normal idle to falter. Use only aerosol carburetor cleaner on the valve parts -- not on the sensors or anything else around the engine area.
Put the idle valve back in place, start the Cherokee and see if this has rectified the problem. If not, take the valve off again and proceed to the next step.
Purchase a new idle air control valve from an auto parts store or online distributor. Make sure to tell them the year and model of your Jeep to get the proper part.
Position the new idle control valve in place and secure it with the two screws you removed earlier. Connect the oval electrical connector by pushing it into place where you removed it in Step 2. If replacing the idle valve with this new one has not fixed the problem, consult a mechanic for further inspection and for advice on possible problems.
