Dr ZEE

Hi guys,
this just happened only once and left me with a mystery and I kind of worry now if there's something I should look into,...
It's 96 I6 auto AW4 200K+

I drove a few miles, so engine was normally hot and everything was fine. So I pulled over a parking space and as soon I shifted to N the engine started racing from "normal" around 1000 to a bit over 1500 and it sounded just like when you press accelerator. This was very strange and I could not miss it. So then I am shifting to R and it stops racing and goes to normal, then I shift to P and it is racing again the same way.
So I shifted few times back and forward and thought to myself: "Hey this is some kind of bad trouble and I better get home asap and see what's going on " ...so without turning the engine off I just went home.
As I got home and shifted from D to N - racing , from N to R - normal, and from R and to P - racing again ...so it did the same thing. So I turn the engine off, and after 5-10 sec. I started it again, expecting it to race right away , but it didn't. And everything went normal. WOW!
So now it does not do this.
Go figure. What the hell was this????? I am so confused

Has anything like this ever happened to anybody? Or maybe it's something simple and common that I just am not aware of?

I have TB all cleaned and have new TPS and new idle control valve.

I am puzzled what should I think of checking?
My xj also has cruise control, which I never use. Not sure if this can get involved here somehow.

any thought, guys?
thanks in advance

jmm0122

Could be the IAC.

rich

Jeep had a paper out about the jeeps engine racing or something similar,maybe check into there recalls or tsbs.

notop46

First off, you have a very sharp Jeep. my only suggestion is to ditch the small spare tire.

I would guess that either your IAC or your throttle was stuck. Check your throttle return spring and cable for frays and keep an eye on it. PU a spare IAC from the JY and keep it with you. Good luck.

Dr ZEE

cool, guys, thanks for your time thinking 'bout this one and sharing ideas.
well, I have a new IAC in there now, I actually have two extra that are used but they also worked just fine... I 've put the new one "just in case" after I cleaned the TB. Also the return spring is clean and lubbed...
Also I am not sure if I understand it correctly, but I would imagine if IAC goes bad it would not "respond" orderly, another words, it would keep for exaple high idle , or go hight-norm in a random fashion or something like that... In this case I was getting race specifically as I shift to N or P.
I din't have a chance to get out and take a look at the TB .... as I expected the problem still be there as I get home, but it just got back to normal after I turned off and restarted the engine.
I have a fantasy about maybe my computer is getting drugged or something ????? I don't know if it's possible, but I sure would not be happy if it's the case ...
It's like part of me is happy that it seems that the problem went away, but on the other hand I feel like got a Ghost in the Machine now, and you never know when this sort of thing may happen again.
*************

Dr ZEE

Huh huh! That's a good one. Right on target
I was thinking about it , pretty much every time I look at it - poor thing....lol , but it Fits nicely in there behind the pass seat

Also, thanks for the tip on cheking the cables ... funny or not, but I totally overlooked this one.

azxj99

i have the same problem and it started when i replaced my tps, weird but the jeep still drives fine just revs up when i throw it in park....

Dr ZEE

Hi guys
just an update here...
so, it looks like IAC was actually the problem. Also I am still not 100% sure, but here's what happened.
Yesterday, I 've decided to "investigate" a bit ..heh heh , though I coud not recreate exactly the same situation, but I was cheking the TB action in PARK by hand under the hood and by pressing accelerator pedal. So the cables looked fine and TB mechanicaly was fine but I've noticed, that (not always but from time to time) when pressing accelerator very briefly (up to about 2000 rpm) and letting it go instead of "normal" pretty quick falling back to around 1000 it would fall to 1200 or so and then would go up for a moment to around 1500 and then slowly fall down to around 1000.
So I've decided to replace IAC with one of the spare I had and after I did this "behavior" was gone
After that So far, no problems.

Thanks again, guys, for leads

Ender

haha, my Jeep revs up like CRAZY when I first start her up, sometimes gets up to 3000 rpm but comes down quick... I think it's the IAC, haven't replaced it yet

notop46

[QUOTE=Dr ZEE;714454]Huh huh! That's a good one. Right on target
I was thinking about it , pretty much every time I look at it - poor thing....lol , but it Fits nicely in there behind the pass seat QUOTE]

I have a 275/75R15 in the factory mounting position. It came in handy when I had a blow-out 150 miles from home.

On the IAC valve: When mine went out, my idle jummped to 2500 RPM and stayed there. I could go through the gears up to 45 MPH without touching the gas petal. I had to shut it off at red lights to keep from scaring other drivers.

Dr ZEE

Hi guys,
I had to dig up this really old thread... huh, it was while ago

But I wanted to let you know what was the problem. So it actually was the messed up Neutral Safety Switch.
When I removed it and opened it up I found it being messed up badly. One of the small copper sliding contact/links was worn down on one side and there was trace of loose copper along the slide-path.
Well, so generally speaking , I guess the switch was confusing the hell out of ECU. I wish I made photos back then ...
So, cleaned it up, file the damaged slide-contact straight, lubed with fresh dielectric grease , reinstalled. The "problem" is gone.

I've made up couple of pics diagrams of the NSS just to attach here for demonstration.

Also there was a good write-up on cleaning up NSS somewhere. Google it

later, guys

/z

jbossnack

this thread ain't dead...yet

My '99 XJ's 4.0 is idling high in Park and Neutral. When it's in Drive it won't idle high, BUT it does idle pretty crappy and sputter a little at low speeds like there is a poor throttle response.

I'd love to get this fixed...any ideas folks??? (I'm guessing TPS and IAC, but what's this NSS talk about Doc?)