DuaneMike

Hello, 1991 XJ 4.0L 5 SPEED has a surging idle when parked or in neutral and sputters or bucks when driving at any speed. The idle sometimes settles down and idles great and drives normally. I've changed the plugs not wires or coil. I've changed the fuel filter, throttle position sensor and crank position sensor. I haven't changed the fuel pump. Please help me if you have an idea of what I can do next. Thank you for your time.

4wheeldrivenewbie

The very first thing is to check your grounds and refresh like in cruiser54's tips also i would make sure your new tps is adjusted correctly like in cruiser54's tips he mentions the proper voltage you should have you can check the sensor with a typical volt meterto see what u have. Next thing i would check your vaccum/harness hoses for leaks.

also you can check the idle air control sensor just 2 bolts take it off and see if it is dirty and clean it off good you could also inspect for wear on the end by the tip and also inspect the sensor connectors for corrosion or anything weird.

One more thing that is often overlooked if your year has a egr valve which i believe yours does as it was the last year of the renix try testing that and see if it is working that could be something

DuaneMike

So I've cleaned some grounds and put a used fuel pump in...still have the surging idle and bucking...forgot to mention I'm not running an o2 sensor...could this be the problem ? I'll be going through the vacuum lines tomorrow. .hopefully settle down the idle.

Oswalla

I never tried running a fuel injected motor without an O2 sensor, but it is kind of important in fuel management by your computer. You might be in a limp mode without it. What you describe is text book- bad O2 sensor. Here I googled it for ya:

The typical signs of a faulty oxygen sensor include increased exhaust emissions due to poor air fuel mixture, engine hesitations, engine misfires, stalling, rough idling and increased fuel consumption. The oxygen sensor is a crucial component of a vehicle's electronic fuel injection and emission system, and it relays information to an on-board engine management computer that regulates fuel delivery to the engine.

4wheeldrivenewbie

yeah that sounds about right he did not mention that at first.

DuaneMike

Thank you very much ...will be buying one from chrysler dealership in Prince Albert saskatchewan Canada ...if anyone's curious and just for giggles. ..the short one 18" is 120.00+tax and the 22" is 180.00+tax...now which one do I buy hehehe....I'm leaning toward the shorter on (less resistance) and cheaper...stock vehicle height ....

DuaneMike

So anyway I didn't replace the o2 sensor yet....but it got warmer outside and now it's running g like a top...please anyone got any insight on this? I will still install an o2 sensor as there isn't one connected right now....but yeah no bucking or surging....the idle goes a bit high and erratic but other than that it's working good...for now.

nujeepguy

my 00 has 2 o2 sensors. one was bad. i replaced it but i noticed zero difference with bad or new?? ran great,still does..

BlueRidgeMark

*sigh* You are missing a major component of your engine's control system and you are wondering why it's running poorly????

I'm tired, so I'm not going to take the time to explain much. You may have two O2 sensors on that year; one in front of the cat and one behind it. Don't worry about the one behind it. Replace the one in front of it. Your car is not going to run well without it.

Basics. Fix the basics.

DuaneMike

Thanks for replying blueridge...I will get the basics down and go from there.

DuaneMike

Ok I've changed the o2 sensor and it still misses and bucks while driving and surges at idle...I'm going to change the cap/rotor and plug wires tomorrow. ..I'll keep you posted ...just in case someone else's 4.0 is doing this crazy dance..!!