cleaning an XJ throttle body?


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Hey guys. My 88 Xj is, yet again, idling thru the roof. I don't drive it that much anymore (only when it rains here in SoCal, if that tells you anything) and right now for the last few drives it's back to it's old tricks: idling at 3k or so in neutral, drops down to 1800RPMs while driving. I live at the top of a big-arse canyon, and it's carried me all the way up the hill many times now, at 35 MPH or so, without ever touching the gas. Ahhh...good times.

So, I know that one thing to try, after I have ruled out holes in vacuum lines, it to clean both the throttle body butterfly and the IAC. I saw this online, and wanted to get a little feedback before I did this myself. This process look OK to you?

I saw many videos just showing folks removing the top 3 torx screws on the top of the flex hose to the top of the throttle body, and spraying carb cleaner down from the top, but then I saw this guy remove the entire throttle body, which seems easy (on video at least) and also allows you to clean the underside as well, and also maybe get to the interior of the IAC a little better (instead of just cleaning the plunger itself?)

One more thing: carb cleaner or AT fluid as a cleaner fluid? I saw someone saying his dealer recommended AT fluid instead? Pros/cons of either one?

Thanks for your time, guys. Wanted to ask first before I jumped into this.


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Carb cleaner for sure, I pulled me completely off also. Not sure on the variations from my 96 to you remix, but I also removed the IAC housing to make sure and get all passages cleared. You might also want to run some seafoam through the manifold.

Have you checked to make sure the butterfly does fully close? Maybe the throttle cable is sticking or putting a little to much pressure on the plate.


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I haven't checked anything except the vacuum lines yet. Good thought though. Might save me some work.


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I haven't checked anything except the vacuum lines yet. Good thought though. Might save me some work.
Trust me, check your intake manifold bolts:
" fishinpolejoe

NAXJA Forum User
Join Date: Oct 2014
Location: North America
Posts: 41

Re: 96 XJ High idle in park/neutral some times
Originally Posted by MACH90XJ
Just curious if ya found a solution ?

Well, since you asked. I was going to wait on a final word before I posted it here but I will go ahead. I'm a little embarrassed that I was too stubborn to even try fixing what was wrong because it didn't make sense to me as a solution.

I'll go back to last Friday. I put on a new IAC as recommended by my mechanic. It didn't help the idle. I don't know if it had anything to do with the new IAC, but my torque converter started working! The more I drove it over the weekend, the better the torque converter worked. During a twelve hour shift delivering pizza on Sunday it started working perfectly and has worked perfectly since.

Wednesday came along and brought with it single digit temperatures. While driving at work Wednesday night, the headlights and dash lights started getting quite dim, the GEN light came on, and the volt meter on the dash was at the top of the red. Seeing as how it was around three degrees Fahrenheit this morning and it barely got out of the teens today, I decided that it was going to the garage instead of trying to fix it myself.

I dropped it off and came back by just in time to watch my mechanic squirt some ether around. Intake manifold, back past the TB, around the next to last bolt, the ether choked it down. Sure enough, a couple of the manifold bolts were really loose and I had a vacuum leak. I asked my mechanic why it didn't idle high all the time. He explained that I had a constant vacuum leak and the IAC was adjusting to compensate for it. He said it would idle just fine until everything got really hot and caused too big of a leak for the IAC to be able compensate for it. It makes sense now and I have learned a couple of lessons.

He said the gasket wasn't blown out and hopefully didn't need to be replaced. I won't know for sure until he gets a new alternator it and test drives it. I will find out in the morning.

Thanks again to everyone for helping. :party:

It is very easy to check for this, but a little dangerous. All you have to do is have the motor running at high idle and spray some ether anywhere there could be a leak. Keep a fire extinguisher handy just in case. If you've never had the intake manifold bolts tightened, check them. Put a wrench on them and see if they are loose. I wish I would have to begin with.

High idle is dangerous by the way. I had two very close calls before I got mine fixed. I wouldn't advise driving it in the rain, gravel or any other loose/slippery surface. Your front tires will lock up when you brake and your back tires will still be turning and it will put you where you don't want to go. Even when you are trying to be careful. Check out the pic in my thread.


New member
I would add that a good cleaning of TB should include the bottom IAC chambers and a new gasket. IAC can be cleaned, I do a rinse and wipe with alcohol after the black crud is off.

Your Renix TPS might need to be re adjusted. Renix TPS is adjustable and needs to be in spec for fuel reasons and transmission reasons. Procedure with specs are here somewhere, search TPS threads.


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Buy aome throttlw body cleaner for the iac and the throttle body of course. Just make sure the sleeve on the throttle body is freely moving and ur pretty good to go. X2 on the seafoam its a great additive especially with this crappy gas we put in our vehicles and all the ethanol now.


New member
Three thousand RPM is usually a major (large) vacuum line, either the one running to the vacuum canister or the brake booster. Or your TPS is full of water. Possible the IAC is stuck full open?

Keep water and solvent away from the TPS, both can cause issues.

I plug off all the vacuum lines except the fuel regulator to see what happens. None of the vacuum lines are necessary for engine function.

Oddities that may cause similar symptoms, but rare, is the fuel regulator leaking raw fuel into the intake. Or rarer still is the charcoal canister being full of fuel and the purge function dumping raw fuel into the intake. Most times when this happens it may idle up in the beginning stages but will eventually bog and spew smoke out the exhaust as the problem worsens.

I'm not a big fan of washing trash down the intake, which may eventually end up in a valve seat.

Always a good idea to check the throttle plate is closing all the way and the throttle cable or gas pedal isn't hanging up. Pretty common for the throttle plate return spring to break, the throttle cable tension will usually close the throttle plate anyway. But they did stick that spring in there for a purpose.

Periodically checking the torque on the intake/exhaust bolts is a good idea anyway. Renix, OBD 1 or 2, they all tend to come loose eventually. Be really careful about torquing the end studs, I usually leave them alone.


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starting fluid or carb cleaner also works well for finding intake leaks.
I've had the best results using a propane torch with no flame, just spewing propane near suspected leaks. A lot less of a fire hazard than spraying flammables around the engine bay. And actually works better than fluids checking for injector O ring leaks.

If you use starting fluid or carb cleaner wear your safety glasses and keep a fire extinguisher handy. I worked a second job in an auto crafts center for most of a decade, somebody would loose most of their hair just about once a week.


New member
Finally got around to this just now. Throttle body was spotless and didn't need cleaning, though I sprayed and scrubbed it anyhow. IAC was...clean. Nothing on the tip at all. I cleaned it anyhow as well, but got nothing on the rag.

So...other ideas? Manifold bolts are tight, no vacuum leaks. Let me ask you this: how does an IAC go bad, and how can you tell? Worth it to try one? Dealer or aftermarket is the better one, if so? I did notice a ring around the brass cone on the IAC, but it is not a groove...doesn't catch a tool or a fingernail. I was wondering if that was a mark of it needing to be swapped out.


New member
On a Renix, it sounds like a bad TPS, or it's ground circuit.

Read Tip 8.

That said, I would do 1 through 5 first...........


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It can get grit and sludge behind the piston. The grease on the threaded piston rod (screw jack) can get crusty. I sometimes spray a shot of penetrating oil or brake cleaner around the side of the piston and flush some of the crud out.
Then I let a few drops of synthetic motor oil run down the side and behind the piston. Very harsh solvents can damage the motor winding insulation or the internal plastic parts.

IAC malfunction is usually one of two things or both. The piston and seat get covered in sludge and get really sticky and/or gritty and/or you have a battery or charging problem or both. In my experience it is a fifty fifty toss up which is causing the issues. One thing I found interesting is battery or charging problems often first become a serious problem weeks after the IAC starts acting up. Grounds, connectors and voltage are also worth a look. It can be a combination of things, poor connections, poor grounds and lees than optimal voltage/amperage.

Messing with the piston isn't advisable, you may screw up the drive motor, the screw jack or worst case you may pull it out far enough the threads on the screw jack don't catch anymore and the spring behind the piston may launch the piston into low orbit. Been there done that.

The IAC is actually pretty tough and seldom the entire problem, dirt and low voltage being the main causes of malfunction.


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The IAC was perfectly clean all around. No dirt or sludge. I just went back out and pulled it again and there's nothing to clean on it.

I see tip#8 about adjusting/testing the TPS. Only one thing: nothing to tell me where the TPS is/what it looks like.