98 xj rough idle and another strange problem

hello,

searched and couldnt find exactly what i was looking for, so dont burn me if the info is here somewhere.

i just got my newest addition to my xj list. it is a 4.0 with 218k on it. runs and drives great but it idles a little rough. nothing to bad, not like its going to die or anything, but enough to be annoying. not sure about when the last tune up was done, but when i pulled the plugs they were brand new, so i dont think it was to long ago. just though someone could give some insight on whats up with it.

also, when the tank goes below 1/4, when you accelerate quickly or you go around turns from a stop sign, it stumbles like it is out of fuel. once you straighten out or let off the gas it returns back to running fine, but it is also an annoyance i would prefer to not deal with:laugh3:

Could be fuel, but it could also be the O2 sensor - I would check the readings with a meter. It can have slow response but not be outright bad and give these symptoms but not throw a code. The corner thing could be a red herring - if turning without slowing/coming to the stop sign doesn't cause the hesitation, the stop and start could be the connection, not the corner.

Plugs could be new because the PO was trying to fix the idle problem with a quick fix rather than diagnosis.

what is a red herring? i have not heard of this. i figured someone was trying to fix the rough idle with plugs and whatnot, but needed ideas to check out.

I always start with tuneup hardware.

You said the plugs are new; did you verify the gap on all of them? Especially important if somebody else installed them. What kind of plugs are they? Plain old Champion coppers work great in your 4.0

Then there are the other critical tuneup components including plug wires, distributor cap and rotor. Not a bad idea either to use a bottle of quality fuel system cleaner to help optimize fuel injector spray pattern. BG44k is my favorite, Techron is not bad either.

See where you are at after those simple things, which probably need to be done anyways.....

The issue with stalling around corners is typically an indication of a bad (or in your case old!) fuel pump/filter.......search on here will bring you some more info

Most likely it is your idle air control valve (iacv) there inexpensive on rockauto.com also the throttle position sensor could be going bad (tps) they both work hand in hand with eachother. i would replace both. the tps is only like 30 buck give or take like the iacv. clean your throttle body before installing them.
hope that helped