Bucking, hesitation, lunging on a cold '99

[vr4operator]

Happens within the first 10 minutes or so. I'll get out of the driveway and sometimes it'll act up, sometimes its a mile or two down the road. It'll drop RPM's like its gonna die, then surge, hesitate, surge, etc. If I floor it (if I have some room) she'll launch forward and it seems to clear. But it'll clear on its own eventually. Seems like once shes warmed up, its ok. And yes, does it at idle.
Did it when i test drove it prior to buying. But looking over everything else, she looked like maybe she sat for a bit and def was behind on maintenance. Air box was full of acorns and dirt, air filter full of crap and rusted, etc. So I figured it was a bad spark somewhere.

Just cleaned and put in a new air filter, plugs, wires, cap n rotor and its still doing it. I'd blame a dirty fuel filter or pump, but they don't give a damn if the motors warmed up or ice cold being back there in da tank.

Any ideas?

Thanks,
Butch

PS haven't gotten around to the drivetrain or changing oil yet. DOubt a dirty tranny filter would cause this kinda bucking, but ya never know with computer cars...

[4.3LXJ]

So, does this happen only when the engine is supposed to idle?

[vr4operator]

So, does this happen only when the engine is supposed to idle?

No, at idle and under throttle. Sometimes going WOT seems to 'blow through' whatever the issue is, but after no more than 20-30 seconds, then its smooth sailing.

Still have the CEL, but its the 455 gas cap code. Got a new cap tonight. Went for the $8 Stant verses whatever the Stealership would get and threw in a bottle of B-12. Gonna disconnect the battery tomorrow and reset is see if it comes back.

[nickxj94]

First thing to do is check all the wiring and vacuum lines under the Hood since there was acorns in the airbox lol it had a critter in there and probably chewed up some of it. Second I would check fuel pressure at the rail with a gauge should have around 49psi at idle. I would look closely at the injectors wiring and may twist the injectors to see if any changes. If it sat awhile tho could just be bad gas especially if its e85 junk, put a bottle of seafoam in the tank with some real gas premium if you can afford it see what it does.

[may pop]

Temp sensor out of specs

[vr4operator]

Temp sensor out of specs

I'm listening...

On the list of things to do (she's new to us), is flush the coolant, replace the hoses and the t-stat. I noted the day we looked at her the coolant was on the well used side.

Could you explain a bit more? I know it ties in with the air/fuel ratio in the brain box. Hmmmm. I looked it up, at 'only' $25, it would be nice to get rid of the headache.

Thanks!

Oh, found out it will do this at idle too, not just going down the road. We changed the oil, and being old school, i ran the motor til she was at normal operating temps. On its way there, the engine did the wanting to stall/high rev back to life thing with no load.

[may pop]

Any codes?
The temp sensor will tell the computer how rich or lean as compared to the engines temp. Richer when cold,leaner when warmed up. Also the OXY. sensors do a similar thing.
Ron

[vr4operator]

Any codes?
The temp sensor will tell the computer how rich or lean as compared to the engines temp. Richer when cold,leaner when warmed up. Also the OXY. sensors do a similar thing.
Ron

I guess I'll try the temp sensor first, its a 1/3 the price of the O2 sensors

[vr4operator]

This vehicle is dragging me down...

Changed the coolant temp sensor, all the hoses, flushed it...and it still lunges and hesitates. Last thing I can think of will be the up stream O2 sensor.

Oh and BTW, who the f!@* designed the petcock? Idiots... so far, other than not being able to lick this problem, the XJ is pretty damned easy to work on.

Hey, does the same year Wrangler shared the inline 6?

Thanks, Butch

[4.3LXJ]

How long has it been since that sensor has been changed?

[vr4operator]

Just changed it today. By your question, I'm going to guess it'll take the computer a few miles to work it out?

[4.3LXJ]

Yes. You could pull your battery cables and touch them together and then reinstall. Then it will start from scratch. These XJ computers seem to learn slow.

[vr4operator]

thats great news, thanks!