nick2326

Ok, so this is kinda weird. First off, 98 XJ, AW4, 4.0L.

So I noticed today while I was trying to figure out where a small rattle was coming from on take-off so to speak...that when I start hitting the brakes hard, coming to a stop, it starts idling real low and really rough...honestly sounds like it is trying to flood. Of the 10 times I did it, it never cut off. Started back up fine. Drives down the road fine. Just when I'm hitting the brakes hard coming to a stop does it kinda sound like it is drowning out.

Any idea?

The brakes work fine. My Dad always said they felt kinda "soft" to him in that you had to mash them kinda hard, but it had always been like that, to me at least. Any ideas?

nick2326

Any ideas?

DFlintstone

Not much help here. The "power" for power breaks comes from engine vacuum. (that big tube) I suppose when you hit the brake there is a momentary drop of engine vacuum. I barely notice it myself, doesn't seem to be a problem on mine. Maybe you have low vacuum due to something else, and the "normal" brake is pushing it down too far? Grasping here!...Idk.

Stabsthedrama

Was thinking the same thing, I'd be shooting down all the vacuum lines and checking for leaks.

CCKen

The PCM/IAC should catch a drop in RPM during braking...I would think.

A TB/IAC cleaning may not be the fix but wouldn't hurt, especially if it's never been done.

nick2326

Yea I have cleaned the TB before and actually checked it today. Had a little carbon on it but nothing bad at all. Checked the main vacuum line coming off the brake booster and it seemed fine. Any other lines I should check? Where is the PCM exactly?

It really only did it when you hit the brakes really hard and like I said, as soon as you actually stopped, and the body jerks to a stop, it instantly comes back to a smooth idle. But during that breaking it idles rough and seemed like a strong exhaust smell like it was flooding.

Thanks for the input.

DFlintstone

The PCM is your puter'. It's located above the water line, (we hope). The IAC is the idle air control. (what we have now instead of an idle speed screw).

Mine is sort of high on the TB, two screws. (TPS is lower, bunch of wires). Be gentile cleaning it, note where the O ring goes. IIRC my O ring stayed in the TB, I needed to get it out and put it on the IAC to install. It's rubber tip, (pintle), is controlled by the IAC motor, which gets it's orders from the PCM. That is what lets air past the throttle plate to control idle speed. If you unplug an IAC it just stays where it is..

nick2326

Ok, I will give it a look. Like I said, I have never noticed it before so hopefully it isn't something that is gonna leave me on the side of the road one day.

nick2326

Well me and Dad just did a little exam on it and still not sure. To start with it was getting worse. Still drove fine but now it wasn't idling good at all. Noticed the check engine light come on as well. I have been having intermittent NSS issues so assumed it was this but wasn't sure. Also have been getting a rattle from my catalytic converter and my exhaust has a strong smell. Per Dad the exhaust was "hot" and "smelled like eggs" lol. So we went to work.

Took off the IAC and cleaned it. Was fairly dirty as it has 232k on it and I'm pretty sure that was the first time it has been taken off. Put it back on. Checked the vacuum lines. They all seemed good. Noticed the O2 sensor where the exhaust bends around the transmission has oil on it. Hooked the battery back up and the check engine light is now off. Don't know if that is a temp reset of maybe if cleaning the IAC did something. Still kinda idled rough though. Put an fuel treatment in it and them rode it to the store and put some 89 in it. It honestly doesn't seem as bad now but idk if that is placebo effect or what. The only thing is that I had about 1/8 of a tank and put about 11 bucks worth (3.5 gals?) in to get where I needed to get Friday. Ever since is when it has had issues with the idle when braking, that progressively got worse (unless I didn't notice it before but I don't think I would miss this) until I put mid-grade, treatment, and cleaned the IAC on it.

So, in conclusion of a long, jumbled post: noticed it wanting to stall out and idle rough after getting gas. Rattle from cat. converter but that has been going on. Now exhaust has a strong smell. Seemed better after adding fuel treatment and putting in 89 octane.

Chance I got some bad gas? O2 sensor? Cat. is clogged? Still bad IAC? or TPS? or MAP? Or a mix of everything? Would like to think it wasn't an O2 b/c that should throw a code...which it did to start with but isn't currently and didn't until the problem got worse. Again, it still drives down the highway fine. Doesn't seem to have any hesitation although it did hesitate when I pulled it to the building for us to look at when it started getting bad...it almost cut off but didn't. Just seems to idle a bit rough and seems like it is flooding when I hit the brakes but right before I stop it goes back to normal.

If you aren't completely lost already, lol, any input would be great as I don't want to start throwing parts on it quite yet as it drives fine.

DFlintstone

Somebody should know more then me....I'd always heard that sulfur smell was a bad cat, don't know for sure though. There is a vacuum test for that. Cruiser has a version in his tips. (found in my sig) The one time I personally found one..lack of power in a Dodge "K" car, loosened the header bolts to allow a leak...WOW!, night and day, power was back, cat was clogged.

Oil on the 02 sensor sounds a little weird. I gather leaving the batt disconnected overnight will clear the PCM. Then it may be less than perfect for a while, getting better each cycle, maybe up to 40 cycles. At least one FSM instructs the teck to take the Jeep for a drive, (a few cycles, on and off), before returning it to the customer. My renix has no memory, that is just stuff I've picked up....

Maybe after it settles down. post up the codes. Ken or someone can likely help.

nick2326

The oil is leaking from the oil filer site (common issue I'm told) and it runs down the pan and kinda sprays back while driving.

Think the difference in oil pressure might be due to the battery being undone for a little while? Or maybe the gauge is messed up. It is reading at like 50 while it is idling while warm...it never used to show that and only has that I have noticed once the weird idle crap happened and we undone the battery. It used to show around 30 or so.

I haven't noticed any loss in power but that smell I always thought was the bad cat sign. It has been rattling for a while and it is getting worse now so I know it is going bad...was just wondering if it would maybe cause it to start running like crap.

Is bad gas too crazy to think?

nick2326

UPDATE: Doing the same thing but got the CEL read and it is throwing a P0171 code. Any ideas as a likely starting point?

DFlintstone

P0171 (M) 1/1 Fuel System Lean A lean air/fuel mixture has been indicated by an abnormally rich correction factor.

No real help here....Do wonder if an 02 sensor wire grounding could cause, "an abnormally rich correction factor."

Over my head!

nick2326

Thanks for the response. My Dad asked a couple friends that are mechanics at his work about it and they both instantly asked which 02 sensor sent the code, lol. Told them there isn't an 02 code but they both said that is what would happen when an 02 goes out. Think it is the upstream one as that is the one that has oil on it and the code read-out said Bank 1 so I'm guessing that would be it? Hoping it is that and not the cat being clogged, which I know it is starting to rattle, but without any loss of power...I hope it is just the 02 sensor.

JackJare9455

My 96 had the original cat on it... I Purchased one of the high flow cats from this vendor.. http://performance-curve.com/thunderbolt-spincat.aspx

Awesome product... It was a good upgrade! I replaced it for being original... not for being clogged. I like to perform maintenance before something craps out on me.