My 1999 Cherokee just started running rough recently. The problem is intermitant, and only occurs within the first mile or so of stop-and-go driving. The car often bogs down when the accelerator is depressed, then surges forward after a few seconds. There is also a noticable click or pop when the car surges forward. I thought it was a backfire, but my wife insists its not.
Any help would be greatly appreciated.
Thanks

 

I'm assuming this is on a 4.0 motor, is your check engine light on? Can you explain this "popping" some more? Any ideas on where it's coming from?

There's a lot of "what it could be's", and it's a lot easier when there's more information given

 

If you have no CEL then you have just 2 possibilities that I can see and they are O2 sensor and the TPS which is just a replacement on your HO motor.

 

Sorry for the lack of detail. Yes, it's a 4.0. No, the check engine light isn't on. The popping noise sounds like it's comming from the rear of the car - i think it is minor backfiring, my wife thinks it sounds more like metal hitting metal.

 

If the popping only happens at startup and comes from the rear only thing it could be as far as I can gather is a backfire..Tells me maybe a timing issue, bad plugs, wires, ...maybe do a complete tuneup if that hasn't been done in some time..I don't know if the 99's have a distributor or not but if it has one then new cap and rotor as well.

 

My 98 is doing the exact same thing.
No check engine codes and I have had the complete tuneup and changed plugs twice now.

I did notice that if i turn the key off and back on while driving it it goes away asap.

I have replaced all the stuff on the motor, tps etc and to no avail.
Let us know if you figure it out, please !

 

update ?

 

Yup...99 was the last year for distributor on the 4.0. 2000 went to coil packs.

 

Updates? I'm having the exact same problem with my 98 grand cherokee including that cycling the key clears the problem. I would love to know what anyone found out might be the problem.

 

I may have figured it out with the help of skibuster's post above. Could it be the ignition switch? That would be a symptom of a bad switch which is in effect turning the ignition off and on rapidly and very short periods of time. This puts raw fuel into the exhaust and when the engine starts the fuel in the exhaust ignites. Accounts for the apperance of rough running and the backfires plus the lack of a CEL.

 

Thanks for getting back so fast BlueXJ. I see where you're going with that, and it does kind of act like its running rich, but if it was the ignition switch shouldnt cycling it while driving make it worse? ie dump more raw fuel while the car is coasting. Besides it only does its fit once per start within a short period after starting rather than intermittently while driving. I'm tending to think something computer or sensor related during the warm up cycle. But I dont know enough about what's different when starting/warming up vs normal driving to guess what that might be.

 

iv recently started building up my 97 grand Cherokee. iv had this same problem for about 3 or 4 years now. and haven't had luck with any one explaning it. my clicking or popping soundle like it is under the hood and when chugging if you hammer it the motor wont rev higher then 2000 rpm shut the jeep off and back on its fixed. also runs 100% better when I put it in nutral.( it is still stock auto trans. )

 

I had similar symptoms a few years back. Replaced the upstream O2S and it cured the problem.

 

I cut the stock exhaust off and took the down stream out my engine light went away and it runs like a dream. makes me whana leave it open header.

 

Please do the rest of us a favor and fix your **** properly...

If you want some help start a new thread in the correct section instead of digging up those from 4-5 years ago about a different vehicle.