On a 2002 jeep grand Cherokee with a 4.0 liter engine what can cause the engine to idle vary low and at times will not idle at all with all of this taking place there are no codes being sent from the?
Could be many things.....Look and listen for any vaccuum leaks around the engine especially up around the fuel injection area. A vaccuum leak will have a high pitch whistling sound. With the engine sucking in extra air at a vaccuum leak this will pull down the engine and affect the RPM's. Run your hands along all of the vaccuum lines to see if you can find a leak. How long since you changed your spark plugs? Most likely it is the Idle Speed Control Valve located in the middle of the engine but on the top surface. If you take off this piece and spray it with Carberator Cleaner 3 to 4 times and let it sit for 15 minutes between sprays it will change things.