96 XJ High idle in park/neutral some times

[fishinpolejoe]

I made up a set of vacuum plugs for the intake manifold a long time ago. High idle, usually around 1500-2000 RPM often means a vacuum line is broken, They don't have to break all the way, they can be cracked and the RPM increase incremental.

I cut short pieces of the appropriate sized tubing around two inches long and plug the ends with a bolt. I keep a set in my toolbox.

Don't fart around, plug them all, and see what happens. If the high idle remains it is unlikely to be a vacuum line issue.

The booster can cause high idle issues. But you will often hear the vacuum leak before it becomes large enough to be an issue, It will hiss when you apply the brakes. I've only seen it once, but the check valve for the booster can fail.

Based on a video I watched, my plan was to blow tobacco smoke into one of the lines to see if it might come out at the leak. It seems too easy not to at least give it a shot. If that isn't productive, I like your method as well. I would need a schematic to find them all though.

The intake can cause high idle issues. Especially if the idle changes as the motor heats up or cools. I periodically check my intake/exhaust bolts anyway. They do come loose. I periodically re torque mine and about half the time find some loose.

There seems to be some variation depending on the engine temperature, but a vacuum leak doesn't seem to fit the bill. I say this because:
I can get in my Jeep, start the already 210 degree engine, and it will idle at 800 rpm. I drive to a customer's house, put it in park, and the RPM's go up to 1,600 and refuse to drop so I shut it off. After the forty five seconds it takes to make my transaction with the customer I restart the engine and the RPMs are back down to at least 1,000 RPMs. I experienced this on thirteen different deliveries tonight consistently. I don't think the engine could cool down enough in forty five seconds for a vacuum leak to seal and the RPMs to return to normal. Would you agree?

Unfortunately I don't have a torque wrench. I'm due for an oil change so I will ask my mechanic to check the manifold bolts for me just in case.

That's right, I don't change my own oil. I'll gladly pay someone ten dollars over the price of oil and filter to do it when it takes them fifteen minutes and it takes me forever. They also grease it, top off the fluids, and let me know if anything looks wrong.

The TPS can cause high idle, usually way high, 3000 RPM or more. I'd be suspicious if my idle went up after getting the motor wet from splash or washing. Spray cleaner can also cause TPS issues, the TPS isn't sealed well.

I've never sprayed the engine off or driven through water more than six inches or so deep. We did get a generous amount of rain a while back.

The throttle body bottom gasket can be a problem, reusing an old seal can be iffy. The bottom of the TB rarely sits exactly where it indented the gasket the first time when reusing the old gasket, there is a little play in the mounting bolt holes.

I intend to get a new gasket when I take the TB off for cleaning which leads me to a question. Do the TB bolts require a certain torque?

Less likely is a faulty MAP, usually when they fail they often richen the motor way up, depends on how faulty they are. The programming is going to try and optimize fuel air mixture and may cause idle issues.

Even the battery temperature sensor can cause idle issues, when mine was bad (in my 96) the idle went up a 100-150 RPM or more. The same can happen with a faulty engine temperature sensor, 100-150 RPM higher because the motor stays in warm-up mode.

Battery temperature sensor? I didn't know that even existed. I put a new engine temperature sensor on it soon after I bought it along with the temperature sending unit because my temp gauge in the dash wasn't working.

Have you tried unhooking your battery cable and rebooting the computer?

Yes. I did that after cleaning the TB and IAC.

I've had good luck spraying a little penetrating oil into the IAC inlet while the motor is running, while I work the throttle a little. Four or five squirts usually cleans everything up quick, just be sure not to lose the nozzle down the TB throat (the voice of experience speaking). The vast majority of the times I've had IAC issues, my battery or my alternator crapped out completely a week or three after the IAC issues first showed up. I don't really know why, but it has happened to many times to be a coincidence.

Ohm test your grounds. Corrosion and old age degrades the ground contacts. Same with the ground crimp mounting rings.

Use the key test to see if you have any MIL codes.

I've run out of ideas, for the moment.

Electricity befuddles me :confused1. I can use a test light, but not a meter. I will have to educate myself.

I will see if I can find instructions on how to do the key test.

I appreciate your ideas!

Joe

 

[fishinpolejoe]

The bolts for the intake/exhaust manifold are a common problem for working loose as MUD8 said above. Why the idle can be effected by a heated up motor is , metal expansion/contraction. To add to the normal expansion/contraction we have aluminum and steel that exp/cont at different rates. At least thats my theory why I have to retorque those manifold bolts periodically.

You should use a torque wrench, buy an expensive one if you can afford it but my old $40 craftsman has worked for me over 20 years. Recently bought a high torque one for my axle/ball joint job. You can put a wrench on the manifold bolts and snug em down without, atleast you can see if it helps your warmed up idle before applying proper torque. Be careful not over torquing, exhaust studs/bolts are usually brittle from constant hot/cold cycles.

A leaking vacuum will always leak. 750/800 rpm is normal idle. Block those lines off like MUD8 said, will quickly eliminate hoses.

I would finish that TB/IAC cleaning job though. I think you know what to expect from half way doing something.

Anything worth doing is worth doing right. Thanks for the tips!

 

[fishinpolejoe]

I had a very similar issue recently, my jeep would randomly try to idle up in gear and if I popped it into neutral it was rev to 1800-2100 rpms. I checked for vac leaks, cleaned the TB and idle valve, finally I hooked up my DRB and found that the TPS would randomly show that the throttle was cracked open when it wasn't. I replaced the TPS and I haven't had any strange idle issues since.

Just and FYI with the JTEC jeeps (96-01) if the ecu thinks the throttle is open it will automatically command the idle valve to fully open, so if you have a bad TPS it will try and idle high.

Did yours run rough though? I'm just curious because everyone I talk to tells me that if the TPS or MAP were bad I would be having much more trouble. Mine seems to run pretty well.

Mine doesn't noticeably try to idle up while in gear. It does pull me up my uphill driveway though. I have to ride the brakes a little to keep from going to fast. It wasn't like that before I had the idle problem.

 

[Original_MudButt]

Not T-case, torque converter.

Sorry, my bad...

It didn't fix the problem I was having which was the torque converter failing to engage at highway speeds, still having that problem.

Time to test your lock-up solenoids. Mine wouldn't go into overdrive on the freeway and it ended up being a bad solenoid.

 

[sidewaysstarion]

Did yours run rough though? I'm just curious because everyone I talk to tells me that if the TPS or MAP were bad I would be having much more trouble. Mine seems to run pretty well.

Mine doesn't noticeably try to idle up while in gear. It does pull me up my uphill driveway though. I have to ride the brakes a little to keep from going to fast. It wasn't like that before I had the idle problem.

Mine ran just fine other than the idle being all over the place.:repair:

 

[fishinpolejoe]

Time to test your lock-up solenoids. Mine wouldn't go into overdrive on the freeway and it ended up being a bad solenoid.

I've been suspecting the solenoids. The TC always engages when I first leave the house and get up to 45 mph or so. Not just 4th gear, it always shifts into 4th no problem. It hits 4th gear and then the RPMs drop again when the TC engages (around 1750 - 1800 RPMs at 55 - 57 mph on level ground). As soon as I bring my foot completely off the gas pedal it's 2,000 - 2,100 RPMs at 55 - 57 mph on level ground for the rest of the day.

Oddly, the TC has started to engage more often since I cleaned the IAC and throttle body. If I let it set for an hour or two here recently it will engage and every now and then it will engage twice before it stops working. I don't know if that has anything to do with the IAC or TB.

Just curious, how expensive of a repair do you think that would be if I paid a professional to do it? Replacing the solenoid that is. There is no way I'm taking the transmission apart myself.

 

[fishinpolejoe]

Mine ran just fine other than the idle being all over the place.:repair:

My idle doesn't seem to be as erratic as what you describe but I find this interesting because I am also having torque converter issues. I certainly wouldn't mind cutting a hole to access the TPS lol! And yeah, that's grass you are seeing through the floor board.

I've been working on the holes. Got them all filled up and covered and some nice diamond patterned, hard rubber flooring down. Still haven't finished the project yet though.

I have all the flooring down except for the driver's side front and rear and the back corner behind the spare. I really like the material I chose.

Talk about thread drift . . .

 

[fishinpolejoe]

I had it scanned today at Advance Auto - no codes.

 

[MACH90XJ]

My idle doesn't seem to be as erratic as what you describe but I find this interesting because I am also having torque converter issues. I certainly wouldn't mind cutting a hole to access the TPS lol!.

TPS is throttle position sensor, bolted to the side of your throttle body. You don't need any more holes :shocked: . Earlier years the transmission was also controlled partially by TPS signal, usually causing late shifts or no upshift. I've had 3 in 10 years go out. 1 was water related. I take mine off when pressure washing motor now.

By the looks of it, I would say previous owner did nothing but drive that thing. Probably have stock spark plugs, haha. Sensors get old and tired like regular maintenance cap n rotor stuff. That throttle linkage probably could use some lube too, I still suspect that.

Pull that TB, clean it, put new gasket. Put new IAC AND TPS. Good preventitive maintenance at the least by the looks of the rest of it. Get a repair book for torque values of that TB.

I am working on wifes 2009 Murano now, never worked on anything this clean. Too bad parts are crazy expensive and hard to find. Cv axle is $700 at dealer, reman is $80 but can only find one on the west coast and $122 for 1 day shipping. Yeh shes driving the jeep for now.

 

[MACH90XJ]

Where did you get that flooring Joe ? Looks good for rear cargo where my lab rides.

Looks like you need a can of that rubber spray as seen on tv. Hey makes a boat shot with a cannon float. I crack myself up....

 

[Original_MudButt]

Just curious, how expensive of a repair do you think that would be if I paid a professional to do it? Replacing the solenoid that is. There is no way I'm taking the transmission apart myself.

I got a "rough" estimate of $500 from the dealer here in So. Cal... The three solenoids cost about $150 plus a trans gasket/filter kit and ATF. You don't have to take apart the trans, you just drop the pan. The solenoids are then accessible. It's easy to do. I'll see if I can find the write-up I used.

Edit: Try here: http://www.naxja.org/forum/showthread.php?t=987463

 

[fishinpolejoe]

TPS is throttle position sensor, bolted to the side of your throttle body. You don't need any more holes :shocked: . Earlier years the transmission was also controlled partially by TPS signal, usually causing late shifts or no upshift. I've had 3 in 10 years go out. 1 was water related. I take mine off when pressure washing motor now.

By the looks of it, I would say previous owner did nothing but drive that thing. Probably have stock spark plugs, haha. Sensors get old and tired like regular maintenance cap n rotor stuff. That throttle linkage probably could use some lube too, I still suspect that.

Pull that TB, clean it, put new gasket. Put new IAC AND TPS. Good preventitive maintenance at the least by the looks of the rest of it. Get a repair book for torque values of that TB.

I am working on wifes 2009 Murano now, never worked on anything this clean. Too bad parts are crazy expensive and hard to find. Cv axle is $700 at dealer, reman is $80 but can only find one on the west coast and $122 for 1 day shipping. Yeh shes driving the jeep for now.

I had read something here about cutting a hole for easier access to a sensor. I thought it was the TPS for some reason. Makes sense that it would be mounted to the TB. :dunce:

I'm definitely going to get a service manual and learn where everything is. I'm going to replace the TPS too now that I know where it is. I believe the IAC is working. I picked up a new TB gasket yesterday. I will lube the linkage for good measure.

The previous owners were a family of rats! That's why I took the carpet out to begin with. I come from coal country and I would bet this vehicle was owned by someone who worked at a coal mine. The chemicals they use in the mines are also in the dirt and mud that employees drive through. Very corrosive stuff. This XJ has seen a lot of road salt as well.

I bought it with 253,000 miles on it last March. So far I have replaced:
Front Brakes - calipers, rotors, and pads
All four shocks
Fan Clutch
Water Pump - had cooling system flushed as well
Engine temp sensor
Temp sending unit
Blower Motor
Blower Motor Resistor
Fuel Filter - I believe it was stock, no kidding.

I'm pretty sure all of those things I listed put together didn't cost half as much as the dealer said your CV axle would be. Makes me thankful for the simple single life.

 

[fishinpolejoe]

Where did you get that flooring Joe ? Looks good for rear cargo where my lab rides.

Looks like you need a can of that rubber spray as seen on tv. Hey makes a boat shot with a cannon float. I crack myself up....

I have a friend in the National Guard. He was part of a supply unit and sometimes they threw things out. He rescued two or three big rolls of the stuff from the dumpster. I have no idea what the intended purpose of the material was but it comes in handy for lots of things.

That rubber spray may have worked better than Great Stuff foam sealant. I was looking at a can of it yesterday and thinking about going back over the holes from underneath.

 

[fishinpolejoe]

I got a "rough" estimate of $500 from the dealer here in So. Cal... The three solenoids cost about $150 plus a trans gasket/filter kit and ATF. You don't have to take apart the trans, you just drop the pan. The solenoids are then accessible. It's easy to do. I'll see if I can find the write-up I used.

Edit: Try here: http://www.naxja.org/forum/showthread.php?t=987463

I may end up doing this if I can't get a much better quote than you did. Link bookmarked, thank you very much.

 

[fishinpolejoe]

I installed a new TPS today and reset the computer. Had to cut one of the torx heads off. Nothing is ever simple and easy. Anyway, I've driven it twice and nothing has changed that I can tell. I started it cold and it idled around 1000. Once it got up to temp it was at 1250. Drove it, put it in park and it idled at 1600. Ate a sandwich, started it again and idle was 800. Drove again, put it in park, 1600 RPM.

I tried blowing smoke into the vacuum lines and found no leaks, the vehicle shows no codes when scanned. I think I might have to give up and take it to a mechanic.

 

[Original_MudButt]

Still, you should check the o-rings at the injectors before you drop the coin. It'll cost you nothing but 10 minutes of your time.

 

[MACH90XJ]

If you checked everything mentioned, there where many but all related to air and fuel delivery.

There is another sensor that has to do with fuel/air mixture, Map sensor. If you got a manual then there should be voltage specs you can check. Maybe a search here will get you testing procedure.

When back probing sensor connectors I have some large 2.5" safety pins I straightened out. Take the pointed end and run it down a connector til it contacts the wiring connector. Then you can get a good voltage read on any connector without unplugging, which is needed in some cases.

 

[fishinpolejoe]

I paid a visit to my mechanic today. I bought the XJ from him and his assistant drives an XJ so I figured they might have some ideas. He believes that I need a new IAC which seems logical. Cleaning the IAC helped it some, but did not completely restore it I suppose. We will see. I plan on ordering a new one tomorrow.

Are there any brands to avoid? My mechanic told me that if I get a new one, it may not work as well as my old one and that I shouldn't throw the old one away. That was a bit discouraging.

On a side note for anyone who doesn't know:
HIGH IDLE IS DANGEROUS!!!
I pulled over onto the left shoulder of a gravel road today to park. As soon as the front tires left the gravel and got in the mud, it sped up, starting sliding, and wouldn't steer as the front wheels were locked up. I had the presence of mind to put it in neutral and it stopped two feet from the edge of a steep bank above a swollen river. I have to get this fixed before someone gets hurt.

 

[Original_MudButt]

Are there any brands to avoid?

When it comes to engine management electronics, I would only buy MOPAR parts just for peace of mind.

 

[MACH90XJ]

My mechanic told me that if I get a new one, it may not work as well as my old one and that I shouldn't throw the old one away. That was a bit discouraging.

If I had a mechanic tell me that I would find a new one., why I don't have a mechanic. A new one won't work as good as a bad one ? WTF is that..

Sensors like that, oem dealer parts are worth the extra dollars. My best tps , that has lasted the longest is from a the dealer, as much as it kills me to say go to dealer. uke: