2004 Grand Cherokee Limited
Start the vehicle and sometimes the RPM will spike instantly at about 2500 rpm. Goes down eventually or when I shift it into reverse/drive.
When I stop at lights or stop signs the engine will jerk sometimes.
RPM will spike sometimes on the highway - going 120km/hr RPM is normally about 2400 but sometimes will spike to 3500+ with no change in speed.

Help please!!

 

IDK what's causing the high idle except possibly a large vacuum leak, but it's hammering your transmission! The sudden change in rpms at speed is probably it shifting out of O/D. This normally happens when engine torque drops below what the PCM thinks is sufficent to maintain speed. Dropping it into gear at 2500 is putting a lot of stress on the clutches.

Check your CCV for a cracked hose or elbow. Also your MAP sensor hose. It also could be the power brake booster, but you'd hear a whistle under the dash.

 

Thanks Dave. Im open to any suggestions especially a quick fix.

 

You can also check/clean your idle air control and your throttle position sensor.