Missing at Idel

I have a 1994 XJ with 140K miles. At idle after the vehile has warmed up the engine will miss perirodicaly while I am ideling at a stop light. Occasionaly, when taking off from idel the vehicle will hesitate slightly. Every thing seems to be fine at higher RPMs and the gas mileage is still consitent.

I think it might be the fuel pump. I replaced the fuel filter and there was black residue coming out of it.

First, could it be the fuel pump? (it is the orginal fuel pump)
If it is the fule pump, how can I tell whether it is the short or long fuel pump?

Tell me what you think.

Anything will be helpful at his point.

Thank You,
Mark

Sacramento, California

Is it the stock 02 sensor? If so, it could very well be that! Also, how are your plugs, wires, Distributor cap and rotor.
And how long has it been sicne you had the injectors professionally cleaned?

What do you mean black residue? Like dirt? If so, drop the fuel tank and clean it out!

MISING AT IDLE

YESTERDAY I CHANGED MY O2 SENSOR ON OUR 89 XJ. IT WAS IDLEING ROUGH AND WOULD OCCAISONALLY STALL IF I GOT OUT OF THE THROTTLE QUICKLY. TODAY THE IDLE IS MUCH SMOOTHER AND HAS NOT STALLED AT ALL. IT SEEMS TO BE A BIT PEPPIER THAN BEFORE. I HAD INSTALLED A REMAN ENGINE IN JANUARY WITH ALL NEW PLUGS, WIRES, CAP, ROTOR, FILTERS, ETC. BUT DID NOT CHANGE THE SENSOR. WE HAVE PUT ABOUT 15000 PLUS MILES ON IT SINCE THEN. IF YOUR O2 SENSOR IS ORIGINAL IT PROBABLY COULD USE CHANGING ANY HOW.

If it's been a while, you might want to run a can of valvoline or other high end injector cleaner. I do so every oil change. Also, deteriorated ignition wires and/or plugs will cause the symptoms you describe.

Read a post recently, about a guy that found the fuel line between the pump and the filter, rotting, was flaking off inside and out (96 XJ).
I´ve found rough idle, often to be multiple problems that add up. Tune up, sticky injectors, 02 sensor are the easiest. Slight vacume leak somewhere will do it also, often along with changes in idle RPM.