2003 Grand Cherokee 4.0, automatic with Select Trac.

Due to the many codes present (crankshaft, miss on 5, 6 cylinder, and major vacuum leak, the dealership replaced the camshaft position sensor and crankshaft position sensor. When this did not fix the multitude of codes (dealership charged $400), I tightened down the obviously loose positive battery cable, replaced the plugs (were worn well beyond their service limits), cleaned all the grounds that I could find in the engine compartment and replaced a broken bonding wire. This eliminated all of the codes except for the vacuum leak, which may have something to do with the filler neck, or a fuel pump gasket. Will look into this later.

However, the engine still shakes, and can be felt shaking the car at idle. There are no codes, no noises, and it seems to run and idle fine. A very quick check of the motor mounts did not reveal anything out of the ordinary.

So, what could be causing the engine to shake? Any suggestions are welcomed.

 

Welcome to CF!

There is no vacuum in the fuel tank except on cold startup when the leak detection pump runs it's check of the vent system. However, there is a vacuum supply hose (tube) from the side of the intake manifold to the canister purge solenoid that might have come off or have a cracked rubber elbow. That will cause a leak and possibly cause the shaking. It's on the side of the manifold just above the fuel line, sort of out of sight. The PCM and idle air control will adjust the mixture and idle speed to compensate for the vacuum leak.

 

Vacuum leaks can cause that as Dave says. Check all the fittings, run down every line, esp on the manifold? After that it's fuel pressure check time, plugs, wires that arc at night in the dark...?

 

did they re-index your cam synchronizer? a cam synchro will cause misfires, cam sensor/crank sensor codes and enging shaking with some hesitation. Replacing the wire may have only fixed your coded temporarily

 

This is an 03 with a coil pack and the cam sensor is just 2 screws and a plug. If it's done right, you don't disturb any timing settings.