POS rough idle
 

I just bought an 89 4X4 XJ auto (with the NP231 transfer case) and it's got a rough idle that drops off intermittently when it's in drive, sitting at idle. I can hear the rpm's drop off but I don't have a tach so I can't see where it's idling. When the rpms drop there is a loud clunking noise that feels like its coming from the center underneath the center console. Occasionally the shake and clunking will continue after I begin accelerating up until I get closer to 2nd gear. I cleaned the NSS today but it didn't seem to help any, could the NSS being bad cause the rough idle or any clunking noises? Or could it maybe be a bad sensor? Any way I can test to eliminate the sensors as the culprit? My backup lights won't come on either but I'm not completely sure whether if the NSS is the reason for the lights not working in the first place. Any pointers for getting my new XJ running better will be much appreciated. :surrender:

Check the flywheel bolts to see if they are loose. Run a can of seafoam per directions thru the engine, and go from there with a full tune -up full change it all. Yes nss is the cause of the backup lights.

is the exhaust hitting under neath because of rough idle

I will definitely check the flywheel and run some seafoam through it, thanks for the suggestion, I hadn't really thought about the flywheel before. Last night I put in all new spark plugs and wires and it helped the rough idle a lot, but it isn't gone completely yet. I checked the exhaust and it had a broken bracket but it still seems to be pretty tight. Also, I figured out last night that when there isn't any weight on the passenger side it clunks really bad sitting in idle, as soon as someone sits down in the passenger seat it stops.

Thanks for the help, very much appreciated.:o

you could try cleaning the iac who knows when it was last cleaned remember its an 89 its gonna have little quirks

Sounds like the '87 I just bought. Sometimes it idles smooth but sometimes it's so rough it shakes the whole truck a bit at stoplights. I assume I need to go through and do a full tune up anyway so we'll see if that helps.

Can the IAC on these Jeeps be cleaned out or is it something you just have to replace? I had a rough idle on my Mustang when I bought it, I cleaned all the carbon out from the IAC with carb cleaner and that fixed it right up.

Cleaner is better
 

After I cleaned the NSS it ran better but it still shakes at stops a little. I found out that my adjusting bolt on the NSS is coming loose. I noticed the threads in the nut were alittle stripped so I think it'll help if I replace the nut. I haven't had a chance (or money) to do much else right now. Its got new plugs and wires...every tiny bit helps the cause. I went through and tightend every nut and bolt I could find. Thank Heavens for the Haynes Manual!

Really? The NSS helped reduce some of the shake during idle? WOW! I may have to get my buddy to let me throw mine on the lift to get my rear brake lights fixed but I didnt think it had to do with idling...

What is the NSS and where is it located? Sounds like I need to check mine. Is there a way to actually test it or it is just a matter of cleaning it and seeing if it helps anything?

NICE CLEAN NSS!
 

It helped more with the bad shifting and the backup lights and shaking while driving, but not at a stop, I think it was more just replacing fluid and the sparks and wires then anything. Also, I've found out the that IAC actually could be an issue for the rough idling and shaking at stops. I haven't had time to check it though so we shall see!

The NSS is the NEUTRAL SAFETY SWITCH and it is bolted to the passenger side of the transmission. It's a triangle shaped piece held in with two bolts. Just clean the inside with a cloth and use a brillo pad on the contacts to get them nice and shiny. BE CAREFUL! if anything breaks it may mean you have to replace it and it costs around $300! It controls the backup lights too so if those are out (after you check the bulbs) it means your switch is dirty or bad. ALSO use dialectric grease on the contacts.

I recommend getting a HAYNES manual. Mine is for the 84-93 Cherokee/comanche. It's really helpful.

BE CAREFUL AND DO NOT LOSE ANY PIECES! THE CONTACTS ARE TINY AND SPRING LOADED AND CAN BE EASILY LOST!:detective:

Here is a link to an article on disassembling/cleaning/greasing/adjusting your NSS.

http://go.jeep-xj.info/HowtoNSSrebuild.htm

The NSS should not have any direct relationship to a rough idle.....

Thanks, I figured it stood for neutal safety switch but I didn't want to assume and be wrong later on. My XJ shakes when rolling to a stop and sometimes when stopped at a light so I'll try cleaning the NSS and IAC along with a tune up. Good call on the Haynes manual, I actually just ordered one off Amazon for $8 a couple hours ago. These Jeeps seem pretty straightforward to work on but I'm sure it will come in handy.

is the exhaust hitting under neath because of rough idle

X2 on this. The exhaust runs above a brace near the middle of the jeep underneath. There is a bracket that holds the exhaust close to the chassis so it doesn't rattle, the bracket is most likely worn out or as in my case, rusted completely through.

I have this issue during cold startup, once its hot the exhaust doesn't hit anymore. I haven't found a jeep I could get under at the JY to replace this bracket the holds the exhaust.

A good bet for the rough idle would be your IAC for sure.Just and idea also would be the throttle position sensor.