Erratic idle is driving me crazy. My 2008 Grand Cherokee (6 cil.)when stopped at a traffic light on "stop & go" in constant rush hour traffic, RPM's suddenly (not all the time) go up and the car suddenly moves forward. It's unpredictable when it's going to occur. If I don't have the brake pedal pushed hard all the time when stopped I could hit the car in front of me when this Jeep decides to do it.
In other ocassions it just seems that the engine is going to die on me, but it has never gotten so bad as to stop the motor. It's an event like in the old days when a carburator was clogged. Dealer has been unable to determine this problem. They have put the car in the computer 3 times. Service manager has driven the car (of course not in the above described stop & go conditions) just arround the dealer and says that it's O.K.
Welcome suggestions !

 

I had a problem like that, my car just stopped, RPM's suddenly dropped, then, well, my cherokee did not suddently moves fordward, but I am pretty sure that your problem is because TPS (throtle position sensor) this sensor control throttle positition telling to the engine when acelerate your RPMs, this sensor is easy to go bad, sometimes because you wash the engine with water, then performance's sensor works erratic, check out this sensor and clean your throttle body including IAC valve, I hope it works out.