Okay so I recently bought a 2004 jeep grand cherokee laredo I6 4.0L 4x4 and just started having some issues. When i go to start it it may take a extra turn but then when it does start it is rough and shakes. In the initial start the rpms jump to over 1 but then fall really low and it will shake. If you put it in gear or push the gas at all while its doing this it will shut off. Sometimes im able to wait and itll ease off the shaking then i can drive it with no issues until i stop or cut it off again. Anybody else experience this that can tell me whats going on so j dont lose my mind blowing money trying to fix it? Thanks

 

change the plugs , wires, cap rotor? fuel pressure?

 

Did that and it only fixed it for about a week

 

I havent checked the fuel pressure yet though

 

Welcome to CF!

I'm just guessing here, but try checking the MAP sensor for vacuum leaks and cleaning the Idle Air Control. Also see if the throttle body is loose on the manifold or the base gasket is leaking. It sounds like you have a vacuum leak, so start with the basics before you replace anything. Check the electrical connections to the throttle position sensor as well. Check the crankcase vent valve hose for cracks or being plugged.

The PCM monitors manifold pressure, intake air temperature, throttle position, and engine rpm to adjust mixture and ignition timing. Just one of these things can be off enough to cause the engine to run rough. The idle air control adjusts the air bypassing the throttle plate to control idle speed. If the piston is dirty it can stick or if the passages are partially blocked with dirt it can cause rough or surging idle. Keep in mind that the throttle body only controls the airflow and the fuel is controlled by the PCM triggering the injector on-cycle time.

 

Remember this engine has a coil pack. No wires, cap, or rotor.

 

Hm. Bad coil pack?

 

Thanks! Ill go through all of this today. Thats great info and helps me alot since this is my first jeep.

 

One thing that will help everybody is if you go to "user CP" and "edit your profile". Plug in your jeep's info so we will know at a glance what we are working with.