I have an 03 grand Cherokee, its throwing a multiple misfire code and a few specific misfire codes on a few cylinders. It has new coil packs installed when bought a week ago, I changed the plugs and no help so far. Any ideas? It runs decent other than the engine bucking while in reverse and it kindave shaking while idling. As soon as you accel it smooth's out though.

 

Could be any number of things, maybe something simple, maybe something expensive. You need to read a bunch of threads on here.

A dirty Idle Control could cause the bad idle that goes away when the engine revs. But so could a weak spark. So could an actual physical problem in the engine, such as a valve not sealing properly. A fast running engine can mask some issues that make it borderline about to die at idle speed.

 

So any suggestions to start? I've done plugs and just did a light seafoam treatment to the intake. May do again with more in a day or two. Thought about trying to change the TPS or CPS

 

Nobody has nothin?

 

What I would recommend is to replace the rubber spark plug tubes that look like cow udders. If these get any kind of carbon tracking on them they will cause a misfire issue.....I have seen this happen and tried cleaning mine, but had to replace them.

 

Bumping with update, I have tried cleaning the throttle body but did not remove it, and that seemed to help some. Also, it seems when I put a fuel injector cleaner or seafoam in the gas after a day or so the shaking goes down substantially or even stops. When it runs out the shaking comes back.

 

Sounds to me you may need a set of injectors. It's possible you got a load of bad fuel that had something dissolved in it that plugged the spray nozzles. To keep it cheap, try a set of JY ones. If they work, then you can decide whether to buy new ones or not.

 

Yea maybe ill give that a try next.

 

So here's an update to my battle with my Cherokee. I took the throttle body completely off and thoroughly cleaned it, including the sensors attached. After installing it ran good with no shaking for a day and then went back to its previous state. I've read somewhere the connections on the pcm may break and cause this issue. What's the fix I hear of people doing with zip ties or soldering? Anyone know or have suggestions?