skidoo

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

UNCC_99XJ

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

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-Tim
-99 XJ Sport - 4.0L - AW4 - NP242 - D30/8.25
-R.E. 3.5" Super Ride
-31x10.50 BFG A/Ts
Hellas, OEM front skid, RE H&T SYE with OEM Front Shaft, JKS Adj. Trac Bar, Rusty's Cat Back with a Flowmaster Delta 40, Magnaflow High-Flow Converter

BlueXJ

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.

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skidoo

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.

okcjeeper

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.

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skiebuster

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 !

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98 GrandCherokee LIMITED 4x4 4.0 auto 124,000 miles and counting.

99 Grand Cherokee Laredo 4x4 4.0 auto, leather, sunroof. 191,000 miles and new motor !

skiebuster

update ?

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98 GrandCherokee LIMITED 4x4 4.0 auto 124,000 miles and counting.

99 Grand Cherokee Laredo 4x4 4.0 auto, leather, sunroof. 191,000 miles and new motor !

UNCC_99XJ

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

__________________
-Tim
-99 XJ Sport - 4.0L - AW4 - NP242 - D30/8.25
-R.E. 3.5" Super Ride
-31x10.50 BFG A/Ts
Hellas, OEM front skid, RE H&T SYE with OEM Front Shaft, JKS Adj. Trac Bar, Rusty's Cat Back with a Flowmaster Delta 40, Magnaflow High-Flow Converter

98JGCL40

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.

BlueXJ

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.

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98JGCL40

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.