Look at my post "stumbles..." same kind of issue. I have change a lot of parts to no avail. If you find it please message me as I have changed just about everything. Going to try the reset thing this week end. Thank God I have had a company truck the last couple weeks.
Item#1. When I left work yesterday, the Jeep acted like it always did. Hit a bump and it stuttered, bucked, stumbled, whatever.
Item# 2. About half way home it stopped doing it.
Item#3. This morning, it was back to its old ways.
The only thing different about yesterday was my trip home. Normally I drive to and from work the same way. Its 14 miles with 3 stoplights. Yesterday I had to run an errand and had to work my way through a lot of construction traffic. So of course it was a lot of stop and go with creeping forward. Most rpms were in the 1500 range, 31Ē tires and 3.07 gears. The PO hand only had it for a year (had a baby, and wife made him sell it) so he didnít know if the clutch had been replaced before. Is it possible that the clutch is the problem? More slipping, heating up or what ever?
Ok, replaced battery yesterday. It needed to be replaced anyway. Old one was 9 years old and Iíve drained it down twice by leaving the lights on. I hoped it might make a difference, but it didnít.
One thing Iíve never mentioned before was that on some bumps when it surged (bucked, stumbled, whatever) it would do it for another second or two after the bump. Itís almost like the gas was being sloshed away from the pickup tube and no gas was getting sucked up. But it does it even with a full tank. This is getting to be embarrassing when people see it doing it.
Still no change. I have noticed that sometimes (no matter what the temp or how long its been running) when I push the clutch in, the idle will drop to about 1500rpm and then slowly drop down to 750rpm, it takes 20 to 30 seconds. The TB and IAC were cleaned within a micron of its life 3 months ago. Could the IAC need to be replaced or has the throttle return spring become so weak that it makes the throttle real touchy causing it to buck with the slighest movement of my foot?
I know a previous poster mentioned how when he got his first TJ it took him awhile to get used to the throttle being touchy. I can imagine mine being touchy but not this much. The only way I can keeping it from bucking is to slip the clutch. I don't like doing that.
How are your guy's spark plugs looking? What plugs do you have in there?
What about the distributor, coil and all the connections between. Are the boots in good shape? Are they staying on tight? No gaps between the plug end and the boot connection?
What about fuel injectors? Are they seated well and are the electrical connections to them good and solid?
Trace all the wiring in the engine bay and look for frays, poor connections and splices, something that would come loose on a bump. Then crawl under the Jeep and check all the wiring there from the engine bay all the way to the fuel pump (and everything in between).
You said you replaced the cam sensor (CMP) but what about the crankshaft position sensor (CKP)? Is it mounted properly in the transmission bellhousing, wires / connections good? Might want to try swapping it for another one.
You mentioned that a new throttle return spring helped. What condition is your TPS in? How about the connections and wiring? What about the IAC?
Geneindenver, what year TJ do you have and what engine (2.5L I4 or 4.0L I6)?
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I originally had a miss only at 3000 rpms, so I made a to do list of plugs, wires, cap, rotor, gas cleaner, clean the throttle body, clean battery terminals, o2 sensors, and coil. I did them in order of least expensive to most, and nothing really helped until the upstream o2 sensor, which when i disconnected it, the miss went away. It took me a while to go ahead and replace it, and in the interim it developed the bump miss. So yesterday I took the plugs, wires, cap and rotor back apart and made sure the gaps were perfect and that everything was nice n tight. Still no change, so the laaaaast thing i did was yesterday after i posted; replaced the coil, and voila! My tj runs as good as new again, and my mpg are way up since basically the entire ignition system is new and/or clean! Ross thanks for your response, I have the champion copper plugs, and everything i did was done per the spec of the Jeep Forum members and they were all right on the money. Makes me proud to be a Jeep owner with this type of community behind me. I've never really worked on a vehicle before, but did all this and a water pump flawlessly with the diagrams and pics here. Thanks again and hope this helps somebody too!