TFitzPat87

So like stated above I have this weird rough idle when the XJ's in park and the heat is on. It's good while I'm driving down the road, and while at stops, but the second I get home or work or something and the heats been running, I put it in park my rpm's drop/fluctuate, and my XJ idles pretty ****ty.

I've done my best to check all my vacuum hoses, and haven't found any loose, missing, or broken. Any idea what is causing this? It really only happens when I put it in park.

Am I getting to that mileage where things are gonna start going bad on me (mileage below)? Like, pulleys, water pump, things of that nature? My jeep wasn't driven too much by the PO, hints the low mileage.

97 Sport, 4.0L, AW4, NP231, 72K miles.

TFitzPat87

Nobody? I know I worry about my XJ, but this has actually been going on for a while. I just got used to turning it off before I put it in park. I just happened to forget I had it on this morning, and when I put the Jeep in park it started idling weird, and the rpm's got all wacky. Turned the heat off and it kinda went back to normal. The heat setting was on the floor, and on low. I didn't have the defrost.

jld66

i have a 97. i run defrost/floor all winter. when i put selector to just floor or dash position. the idle drops a bit. have lights, no tach so can not say how much. i think maybe the selector switch may be on its way out. but in defrost/floor, it is fine so i just leave it on that.

Potatowalker

I'm no expert but here's a thought or two: With defrost/floor or defrost selected, the a/c compressor kicks on so that will affect the rpms briefly from what i've noticed on the XJs i've had. Try using just floor or dash vents and see if that makes a difference. If not, then maybe it is a vacuum thing. I'm pretty sure the bad pcv gaskets i have are creating a pressure leak and i think it is affecting my AW4 shifting and idle slightly. Gonna do the Valve Cover and those grommets soon to see if that's it since it's starting to seep at the VC anyway.

TFitzPat87

Thanks guys, thought I would never hear anything on this.

It happens regardless of what the heat/ac selector is on. I don't have to run defrost/fog much, so it's usually on floor. Get to work/home, put it in park and idle goes funky. Can't figure it out. Fine when in drive/reverse, only happens in park.

Replaced the ccv and grommet about a month a go. Didn't change the one in the front (closest to grill), it's still tight. As far as I can tell after inspecting as much as possible, the vacuum lines are solid.

C H E R O K E E 98XJ

Another thing to check would be the Idle Air Control (IAC) on the throttle body. Those are notorious for getting gunked up and can cause a bad idle speed. Taking the throttle body off and cleaning it as well as the IAC is not a bad idea at all and is very easy to do.

TFitzPat87

Done that as well. Gave the whole thing a nice cleaning a couple weeks ago.

C H E R O K E E 98XJ

How about injectors, spark plugs, wires etc?

TFitzPat87

I think my injectors are ok. I'm averaging 18.5mpg (25% city, 75% highway). Still want to put 703's in though.

Changed plugs, wires, distributor cap, and rotor last October. Actually just yesterday I pulled all the wires, made sure plugs were tight, and added dielectric grease to all the plugs.

Potatowalker

I was gonna say that too, but since you checked i guess that's not it. Next few things I'd check are: how old is your battery and are the connections clean? How old is the fuel pump? and just because no one has mentioned it how about the air filter? Also, did you check the plugs and their gaps by removing them or did you just make sure they were tight?

TFitzPat87

Batter is from 2012, and I have good power/charge. Fuel pump... isn't that in the gas tank? I can only assume It's the original, but considering my mpg is good, I would think that's not an issue. Air filter was changed along with the oil change. Gaps on the plugs were confirmed before original install, however, I didn't pull them this past weekend to verify, but I would think they haven't changed.

I'm not all that worried about it, it just seems odd, and would like to fix it. I would understand if it happened with the defrost or ac on, but not when it's just blowing heat on the floor.

Appreciate all the ideas, guys. Anyone have a diagram of the vacuum lines? I checked what I could see, but maybe I missed something, or need to remove some stuff to get a better look.

Potatowalker

one other thing to look for on vacuum lines: my friend had a 2000 that had some kind of rubber cap on a stud on the side of the intake manifold that got knocked off or fell off. The stud it was on is for a vac. hose attachment so when it came off it caused a leak. Wasn't easy to notice right off, but gave him all kinds of issues until he found it.

On my old 96 the fuel pump started to go bad, but it didn't quit outright. It just got weak and then the check valve failed in the pump so it would start hard every morning or after sitting for more than 30 mins. Before the check valve went though it ran/idled rough and low but still started and ran. After I replaced the pump assembly in the tank it ran better than it ever had before, noticeably. Never affected mpg at all that i could see. I figured that out using a fuel pressure test kit for a few days of random pressure reads. Just something to keep in mind.

CCKen

This is an odd one.


Does it act up if you put it in neutral instead of Park?


I don't know at this time what it will prove, but remove fuse #6 from the PDC. Fuse 6 feeds the HVAC blower. Any time the mode selector is in any position except OFF, the HVAC Blower is powered.


Try removing fuse #6 and see what happens.


The P/N switch (part of the NSS) is grounded at G106, which is located on the left inner fender, just below the windshield washer filler cap. The Blower is grounded at G108 which is located under the dash on the far left side. As you can see, both grounds are chassis grounds.

TFitzPat87

Thanks, Ken. I'll have to give that a try. I thought this one was weird too. I'll try and make it happen again, and maybe pass on some more detail.

Since you brought up the NSS, I noticed my reverse lights delayed to come on when it was cold outside, but my XJ always started in park. Then when it was REALLY cold, it would throw a CEL and I had no OD until I turned it of for a couple minutes, then back on and OD was back. This only happen 3 or 4 times all winter. This past weekend, I wanted to take it off and give it a good cleaning, but for the life of me couldn't get it off the shaft. Anyone have any ideas on hoe to get it off without breaking it? Considering it works fine unless it's crazy cold out, I don't want to damage it.

CCKen

Summer's coming, leave it be for now.


if it still acts up when in Neutral instead of Park.